They'd all been exposed to it. More than once, actually - a stray drop here, a brush with their skin there...not to mention the countless hours spent in close quarters with them. They'd breathed them in, and in the end, that's all it took.
Sam was the first to be affected. It wasn't surprising really, given his current mental state and his unique body-chemistry.
He woke up, and went on his morning run. Since his wall came down, his mind's default setting had been a slowly simmering madness. He had to fight actively to differentiate between his hallucinations and what was real. He had to remember that he wasn't burning, that Lucifer wasn't really running next to him, or after him, or ahead of him (backwards). Today though - there was nothing. No struggle, no Lucifer, no torment...just clarity - the kind of clarity he'd always longed for. Before today the closest he'd gotten was a few minutes of near-calm at the end of a run. Today though - three minutes into the run, everything clicked, and Sam understood.
Dean was on his second morning shot of whiskey when Sam came back in from his run.
Sam eyed Dean's glass and rolled his eyes, "You're pathetic."
"Excuse you?" Dean snapped.
"It's 8:30 AM, and you're drinking. You're an alcoholic. A functional one - well mostly."
"What the hell crawled up your ass this morning?" Dean yelled.
Sam scoffed, and walked past Dean without another word. He finished up his workout - push-ups, pull-ups, sit-ups, and went to take a shower.
Dean took one look at Sam, freshly showered and smug, and felt his hand curl into a fist. He slammed his glass on the table and stood up. "You think you're better than me?" Dean growled.
"I know I am." Sam said, smirking.
Dean threw a punch, aiming for Sam's face, but Sam dodged his fist easily, and grabbed his forearm, twisting him around into a headlock.
"Pathetic." Sam said and chuckled, "I really don't know why I never did this before. Guess I thought I deserved it, all those other times."
Dean grunted and kicked back against Sam's shin.
Sam winced, but didn't let go. He tightened his grip around Dean and squeezed. "You know, I was gonna just leave - just pack my bags and go. We could have avoided this, but then, this is you we're talking about." Dean's skin was starting to turn a deep shade of purple. Sam let go of Dean and watched him fall to the floor with a heavy thump.
He crouched down, picked Dean up and slung him over his shoulders in a fireman's carry. He nudged the door open with his hip and walked outside, behind the cabin, to the hill. He laid Dean down on the ground and shook his head, "You know what the funny part is? Turns out I'm not crazy." Sam put the tip of his boot on Dean's torso and pushed up until Dean started rolling down the hill, leaves crunching noisily in his wake.
Sam walked down the hill after Dean and sat down next to him. He picked up a stick and started peeling off the bark. "I mean yeah, I see things - all the time, but it's not me. It's Lucifer. He's in my head." He tossed the little bits of bark onto Dean's bloodied face. "You're a vessel too, but...you never said yes. Lucifer can dial right into my lobes any damn time he feels like it. He's trying everything to bring me back downstairs to him." Sam laughed, "I don't want to go though, I mean especially now. " Sam grinned, "It'll happen to you, too. It's already started, but soon - probably in a few hours give or take - things will be different. It might not be as easy for you though. Lucifer protected me from the worst of it. He still thinks there's a chance, you know." Sam laughed again, loudly, "He really thinks he might get out again one day, and when he does, he needs me to be intact and human - well, as human as I've ever been, anyway." Sam tossed the stick back into the leaves and stood up. "I'm gonna go. I know you probably didn't hear anything I just said, and I don't really care, but in case you are hearing this, do yourself a favor - don't come after me."
Dean woke up to find Bobby staring at him.
Dean brought his hand up to his head, which was throbbing with a low but constant ache. "Bobby?"
Bobby's blank expression turned into a sneer and he pulled his hand back into a fist.
Dean reacted faster than he thought he could, caught Bobby's hand in his own, and brought his other arm in front of him, blocking Bobby's other fist.
Bobby opened his mouth, unnaturally wide, and hissed at him, his bifurcated tongue reaching out toward Dean.
Dean let go and recoiled in horror, "Bobby, what the hell!" He should run, he should want to run at least, but...he didn't. He stood up, backed away a few steps and then froze.
Bobby got up and came towards Dean, still hissing.
The oddest sensation, something like a dozen tumblers falling into place at once, swept through Dean and from one second to the next, all his confusion and horror just fell away. The only thing he could still feel, was hunger. He looked at Bobby, and opened his mouth wide.