"If you tickle us, do we not laugh?" – William Shakespeare

Reid had absorbed enough popular culture to know wearing your romantic partner's clothes was generally well received. He also did it because he enjoyed it; he never wore Morgan's clean shirts, because that defeated the purpose, it was always something Morgan had already worn. It meant it smelt of his lover, the rich smooth smell hugging him. That was what he was currently indulging himself in, as he paced slowly around their bedroom in his boxers and one of Morgan's big shirts, holding papers in one hand while the other hand the shirt sleeve pulled over it and was pressed under his nose so he could breath in the man's scent.

"Do you remember the first time you wore one of my shirts?" Morgan asked, leaning against the bedroom doorframe. Smiling, Reid looked up from his papers, coming to a slow stop and absently rubbing his foot over the back of his other calf.

"Yes."

"It was the fourth time you stayed over-"

"Sixth."

"Sixth time you stayed over." Derek corrected. "And we were lying in bed, and you must have thought about it for fifteen whole minutes – I could see the cogs working in your brain and you kept looking at my shirt on the chair – and then you asked my permission to wear my shirt."

"I didn't think it would be polite to just put on someone else's clothing."

"I don't mind."

"I know you don't now."

"You look so good in it, baby." He cooed, stepping into the bedroom proper and pulling off his teeshirt, his loose sweats low long on his hips. "C'mere and let me make love to you while you keep the shirt on. I know you love that."

"Sounds great." Reid smiled, but then shrugged. "But I'm reading."

Morgan narrowed his eyes at his lover; he could not be brushed aside so easily, especially when Reid's decline, he knew from experience, was meant to tease him.

Reid felt the slight brush of fingers against his side, and having not expected it, couldn't temper his reaction before he thrust his middle forward away from the contact, with a small meep of a noise. His eyes slid sideways, and he was greeted with Morgan's widening smile, and he knew what was coming, so he ran.

He didn't really have anywhere to go in the bedroom, and his brain had conveniently displaced the location of the exit, so he clambered over the bed, dropping his papers on the way, hoping it would shield him. Morgan didn't move so fast, because he could already see that Reid was backing himself into a corner.

"Tickling has been observed as a legitimate form of torture." Reid swallowed nervously, holding his hands up defensively as the older man stalked around the bed, a distinctly wolfish quality to him. Reid's pink tongue snaked out to wet his lips nervously, shooting the man a grin and hoping that would be enough to convince him to back off. "Its use in the Flossenburg concentration camp was recorded by a homosexual prisoner called Heinz Heger, and- Derrreeek!"

Hands that knew the other's body connected and performed fluidly in just a few seconds; one gripped his waist firmly and pulled him towards the bed, a knee helping to unbalance the slender man and deposit him on his back on the bed, while the other hand pushed the shirt up Reid's torso and stretched out fingertips and ran them in rapid brushes over his side.

Giggles exploded from Reid and his writhed, trying to move away from the contact but unable because Morgan's hold was impeccable. His arms became useless, curled up against his chest, fingers crooked like birds claw as his back arched.

"Morgan!" he managed through giggles. The contact had disabled him so much that Morgan loosened his hold, using the other hand to mirror the assault on his other side, hands sometimes tickling over his belly as the younger man writhed. "Morgan, please!" he begged, laughing and panting.

"What was that about tickling as torture, sugarbutt?" he teased, grinning down as he witnessed Reid's face and neck beginning to flush pink.

"Deeerrreeekk!" he pleaded, arms finally cooperating with his brain and slapping at Morgan's arms, attempting to stop the assault of fingers twisting over his sensitive skin.

"Ah-ah." He chided, grabbing first one thin wrist and then the other in the same hand, lifting and pinning them above Reid's head to what he knew somewhere in the back of his mind was not the full resistance the other was capable of. Indeed, Reid could have used his legs to fight if he felt in danger, but as it stood, Morgan had stopped tickling him for a moment and Reid was laid panting, a few token struggles against Morgan's strong grip on his wrists.

"In ancient Japan," he panted as he felt Morgan's fingers dancing up his side, not quite enough pressure to tickle outright, but enough to make his skin itch pleasantly, "kusuguri-zeme was a form of torture. Merciless tickling."

"Oh, I have mercy, baby." Morgan purred. "You're just so cute when I'm tickling you like this."

"Knismesis." Spencer breathed.

"What?"

"That's what you're doing." Spencer pushed his hip a little into the contact, the light swirls of Morgan's callous fingers over his sensitive flesh. "The tickling sensation is two separate types of phenomenon. Knismesis is what you're doing; light touches that seldom produce laughter as a response, but have been linked to sexual arousal."

"Arousal, eh?" Morgan chuckled, snaking his fingers higher, pushing the shirt up as he went. "What's the other one?"

"Stop." Reid said, fighting the smile teasing at the corners of his mouth and looking up under heavy eyelids.

Morgan smirked and shook his head, and suddenly tickled the man right under his arm. Reid burst into high pitched giggles and squirmed, trying to lower his arms and shield himself, but it was no use with Morgan gripping his wrists above his head.

He was breathless again in short seconds, back arching and hips snapping upwards, motor control compromised by the stimulation. He tried to will himself still, to convince his brain this stimulation shouldn't make him react, but it was useless.

Morgan, however, misjudged, attempting to swap the hand he was using to restrain his lover. With a simultaneous firm knee just beside Derek's groin and the twisting of his wrists he got his hands free and shoved the other man off him, immediately straddling his hips and grabbing both of his wrists and pinning them to the bed, hard.

The older agent's cheeky grin faded quickly to worry, as his brain quickly considered several things; he may be physically stronger, but there was a good possibility Reid would get his fingers against his ribs before Morgan could reassert a dominant position. He also didn't want to use all the strength he had, because it was Reid and it was unspoken that this was play, and for it to be fair Morgan had to hold back. But the thought taking up most of his brain power was that he had no idea how ticklish he was. The rare occasions where tickling happened, Morgan used it to incapacitate the other, because it was adorable. But here he was, with his beautiful lithe lover straddling him, grinning rather smugly at him.

"The other phenomenon of the tickling sensation is called gargalesis." He informed his partner. "Only humans and some primates have been proven to be able to sense the difference between knismesis and gargalesis."

Reid's move was sudden, and Morgan's reaction unexpected. Reid danced his fingers firmly over both of Morgan's sides, and the man let out a strangled sound between a laugh and a grunt, attempting to bend double with such force he almost dislodged his lighter partner. Spencer rode out the motion, tickling the soft taunt skin of Morgan's middle, watching as the man twitched and writhed, his arms flailing and locking alternately. His barking laugh soon rose in pitch, becoming an uncharacteristic giggle. Reid had never seen such unbridled reaction from his lover.

"Baby!" he squealed as long thin fingers played along his muscles, making him feel like his skin was tingling with electric current. "Spencer! Spence!" it sounded like a plea now, but the other man was so intrigued by the sounds and response he was eliciting he didn't let up, even as Morgan rocked and tried to dislodge him. Reid started to giggle too, the sound infectious.

"Wow, Derek," Reid laughed as he continued to tickle him relentlessly, "maybe you're hypergargalesic. Isn't that handy to know? Any time you try to distract me with your penis I can neutralise you."

"You- want – you – dick-" Morgan was trying to form a retort, but it was impossible as he giggled madly and gasped for air.

"I want what?" Reid teased, prodding the man in the stomach with one hand and making him huff with the sensation. The man's body was warm below him, his hips and thighs strong between Reid's own legs. With a sudden surge of his full power Morgan bucked Reid off of him, stopping his assault and planting him on the bed. Instead of looming over him as before, he wrapped his arms around his knees hard, stroking a hand down to the man's feet, which made Reid suddenly still.

"I was going to say," Morgan panted, "why would you want to 'neutralise' me when I'm distracting you with my dick? You love my dick."

"I love you." He corrected. "I enjoy your penis, but have no romantic feelings for it on its own."

"Don't think flattery is going to stop me." Derek chuckled, dancing his fingers over the top of Reid's foot. The older man had been surprised to find his lover's feet so sensitive, and knew what the briefest touch would bring out of him. So Morgan firmed his hold around the man's calves and tickled the bottom of one of his feet, relishing the sudden squealing mad laughter and squirming fight as Spencer tried to wriggle away from the overstimulation.

"Derek!" he pleaded breathlessly. "Derek, please!" his words seemed sincere in their plea, but they were distorted with his intoxicating giggling, and Morgan didn't need to look around to know the sensation left the man prone and useless. "Oh god! Morgan!" a sharper cry as the man switched feet, and a groan and increasing giggles as Morgan chuckled along to his own torture.

"Tell you what," Derek started, reducing the movement of his fingers a little, leaving Reid still giggling and writhing, but not so much he was having trouble breathing, "answer me this, and I might stop. How come you can't tickle yourself?"

"Erm, ah-" another set of giggles, though Morgan had relented even more to enable him to speak. He studied the man's back, his face in profile and smiled breathlessly to himself as he considered just how wonderful it was that they were here together. "Actually auto-knismesis is possible. I mean when you run your hands on your skin you still get a shiver..." Morgan looked around, grinning at him in time to see him flutter his eyes and titter with embarrassment. "But MRI scans and use of a self-tickling machine have shown that we don't respond to the touch when we know where it's coming; cerebellum sends information on the intended placement of the pressure to the somatosensory cortex so the body expects it, and a cortical mechanism inhibits the tickling sensation. Tickling administered without the subject knowing where they're going to be touched is the most effective because of this."

"Wow." Morgan nodded. "That's interesting. But..."

"Derek! You promised!"

"No I didn't. I said I might stop." Morgan teased. "And it's even more fun to do, knowing the science behind it."

Reid groaned, and then the tickling started again, making Reid jump and whimper and laugh all at the same time.

Morgan would think later he had underestimated Reid; when the opportunity came – just the slightest release of the hold Morgan had – Reid drew his leg back right up to his chest, and just as quickly flung it forward, planting his foot flat on Morgan's back and knocking him forward. Reid was no athlete but he had long, strong legs, and being kicked by him was rather like being kicked by a giraffe. It knocked the wind right out of Morgan, and coupled with the surprise he ended up falling off the end of the bed into a heap on the floor. Reid scrambled to follow him, planting himself again on top of his lover and attacking his middle with his fingers, delighted to hear the rush of giggles start up from him again.

The other had more fight in him this time, rolling them and swatting the man's hands away, enough to get his own against Reid's sides and render him incapacitated with laughter, at least until Reid was able to perform exactly the same motion and resume his tickling assault on his lover. Soon their giggling at stimulation, and laughter as a response to witnessing and causing the former in the other was indistinguishable, a mess of limbs rolling around their bedroom floor.

Eventually some of the fight went out of Morgan, who was more effected by the action, and Reid was able to pin him, tickling him mercilessly and delighting in the man's breathless, wheezy giggles as he struggled to take lungfuls of air.

"Reid!" he gasped. "Reid! Stop! I'm gonna pee! Please!"

The man finally relented, knowing it was an admission of defeat, and he watched as Morgan collapsed, breathless with residual giggles. Spencer went with him, pressing his lips to his collar and running his hands flat and smooth up his torso, along the oversensitive skin.

"You're really ticklish." Spencer kissed his shoulder and then his neck.

"I swear, if you tell anyone-"

"Now why would I give anyone else that kind of power over you?" he teased. "Can you imagine if I told Garcia?" Morgan groaned.

"She'd love that."

"I think it would be amusing." Reid said. "But long term, I'd rather only I knew that trick to get you squealing."

"I did not squeal."

"You did."

"Did not."

"Do you really want me to prove that you did?" Spencer asked, wiggling his fingers in front of the other's face.

"No." Morgan said as he rolled them, slotting himself between Reid's legs and wrapping his arms under and around his shoulders, cradling his head and bringing them close together. Spencer hummed in content and hooked his legs around the other, arms mirroring the other's action and smoothing over his neck and crown. Morgan lowered his mouth to kiss him softly, big full lips smooth and sweet against him. As he pulled away, he expected some romantic sentiment from his lover who looked at him with such adorable and warmth.

"I can feel your hard-on."

Spencer snorted out a laugh, automatically flexing his hips upwards against the others, finding a matching bulge.

"We have just been rolling around on the floor together." He informed, lifting his mouth for another kiss that Morgan had no thought to deny. "And there was penis talk."

"You started that." Morgan reminded him.

"I know," Reid muttered, lowering his hands along the man's back to grip his rear and pull him closer against him, "with the intention of finishing it."

"Glad to hear it." Morgan smirked, rocking his hips and pressing his lips to his lovers, feeling the coil of heat tightening in his belly to match the feeling that always lay in his chest, one that was given strength by saying its name. "I love you, pretty boy."

"Those who tickle themselves may laugh when they please." – German Proverb