Okay, I have no idea where this came from. It's crack, has nothing to do with The Long Road Home in any way, and I had fun writing something with this level of pointlessness. Enjoy.
If asked about it later, Bumblebee would deny he ever had a part in it.
In truth, he had started the whole thing.
Mirage was newly arrived to Earth, and after Ratchet had given him a thorough diagnostic, Mirage was released into the Nevada night to secure an alternate mode under cover of darkness. Sam and Bumblebee happened to arrive at the base just as Mirage was leaving the medbay, and the spy was naturally curious, getting his first look at their new home's native sentients. It was a very ordinary introduction until Sam sneezed.
Bumblebee, from the very first time he'd witnessed this phenomenon, thought it was one of the funniest things he had ever seen. A human sneezing could go from grave and somber to spastic and ludicrous in nanoseconds-- the face would contort, the teeth bared, eyes clamped tightly shut, sometimes the entire body jerking into a parody of itself for one instant before returning to normal. It was really something to watch.
And every human was very peculiar about their individual sneeze. Sam's came in pairs, without fail, and before there would be a long anticipatory yawn-like intake of breath, during which the boy would tense, hunch his shoulders, and splay his hands as if to flail for support. Then the sneezes would explode out of him in rapid-fire succession, flinging his upper body forward. And to say nothing of the sounds that came out of him during the whole display--!
Mikaela's sneezes were a great deal less theatrical; she would sniff uncomfortably for a few moments before turning her head aside, sometimes covering her face as she did so if she had a tissue at hand. Glen, through some genetic quirk, would sneeze when exposed to sudden bright light, a discovery that led to the poor human being repeatedly ambushed at night by Sideswipe's (and occasionally, Cliffjumper's) high-beams. Maggie's sneezes were high-pitched, quiet squeaks. Lennox, by contrast, bellowed like a beast when he sneezed and could be heard through walls.
The general consensus among the Autobots was that the sneeze was highly amusing, though most of them, out of politeness to their human allies, did not show their feelings outright. Bumblebee once remarked to Sam (after a particularly satisfying double-achoo) that sneezing was an odd sight, given that a Cybertronian's body had more efficient, less noisy ways to deal with foreign elements. Sam had merely shrugged, wiping his nose on a spare napkin hastily plucked from a nearby Burger King bag.
"Check for brains," the boy had said, and grinned up at his guardian. "When I was little, some kid at school convinced me that if I sneezed three times in a row, my head would explode. I think I believed that for longer than I believed in Santa Claus."
"Check for brains?"
"Kind of an in-family joke, I guess. Instead of 'bless you' it's 'check for brains' in case you sneezed so hard they might have come out."
"... my dad's sense of humor. You don't want to know what he says for burping."
So when Sam let out his twin sneezes there in front of Mirage, Bumblebee thought nothing of casually reminding his charge to, well, check for brains. Poor Mirage just stood there for a moment, looking uncertainly between Bumblebee and Sam, unsure whether to be amused at the sneezing or alarmed at the implication of brain matter loss.
"It's called sneezing," Bumblebee explained, transmitting some basic data. "It's a perfectly natural function to clear the respiratory intakes."
And then, he got creative.
"But there's a danger of explosive cranial inversion, you see, if there are too many sternutations in quick succession. Which is why it's traditional to advise a human to make sure there aren't any preliminary leaks."
The shocked look on Mirage's faceplates was certainly priceless, but the spy was too canny to buy Bumblebee's mischief for very long. One look at the internet was all it took, really. That, and Sam's fit of paralyzing laughter.
"How very droll, Bumblebee," Mirage chided in good enough humor. "Harass the newcomer. If you'll excuse me, I must locate a suitable alternate mode. Sam Witwicky, my deepest apologies for your having fallen in with such a shameless rascal."
It wasn't until the next day that Bumblebee realized what he'd started.
"Oh yes, it's true," he overheard Mirage saying to Trailbreaker and Wheeljack, who had likewise recently arrived. "I witnessed such a tragedy in town, just after I scanned the vehicle. Quite gruesome, quite. The poor thing didn't check for brains."
And as if it had been rehearsed, Sergeant Epps walked by the gathering of newcomer 'bots, and sneezed. The resulting two-robot flinch of horror startled the oblivious human, who quickly became unnerved having Trailbreaker and Wheeljack stare in morbid dread, waiting for his head to explode.
"Check for brains!" Trailbreaker desperately implored, and suddenly Epps found a reason to be very, very far away.
"Now who's shameless?" Bumblebee accused laughingly, after letting the two others in on the joke.
Word got around quick, though, quick enough for Prowl to issue a stern base-wide no-exceptions ban on the phrase "check for brains" (in any language) shortly before a visit by Secretary Keller. And things were fairly calm until the arrival of four more Autobots.
Wheeljack managed to convince Springer that the sneeze was a human mating call. Ironhide disabused him of that notion before it got too far, fortunately.
Sideswipe enlisted Glen in the hazing of the notoriously high-strung Red Alert, offhandedly mentioning that a human who sneezed more than twice in one day was actually speaking in code to other sneezing humans, and any sneezing human was a part of a global secret society called G.E.S.U.N.D.H.E.I.T. The pair even went so far as to create a website claiming to expose the conspiracy (all in 14-point blood-red Comic Sans, for some reason) in hysterical alarmist tones, and then manipulated Google rankings so that it would be the top result for an internet search for the topic of sneezing when the hapless Red Alert tried to verify the claim.
Sideswipe's internet access was summarily blocked, until such a time as Ratchet felt he had learned his lesson.
The hazing died down, but soon after Sunstreaker took it in his processor to start ranking the humans' sneezes, and Bluestreak happily joined him. 1 being 'pitiful' and 10 being 'quiet, you'll wake Primus.' Sam consistently scored 8-9.7 for his, to his delight. Lennox was less than amused at being given enthusiastic and awestruck 11s. Mikaela soon grew annoyed with Sunstreaker tsk-tsking her "weak 3, 3.5 at best, can't you do better?" sneezes, but Bluestreak won her back by jokingly offering to help her improve her score by kicking up some dust.
Epps, who still wasn't in on the joke, couldn't figure out why robots were randomly yelling numbers at him.
As jokes do, however, it aged and petered out eventually, the normalcy of their strange, beautiful, unpredictable new home taking hold once more. And during one particularly dicey battle with a group of Decepticons, help arrived in the form of Kup and his group, having literally fallen out of the sky just in time. Thus bolstered, the Autobots made short work of the enemy, the more cowardly ones scattering like turbomice.
"Kup, old friend," Optimus greeted warmly, once all cannons had cooled. "It is very good to see you again. Welcome to Earth."
"Weird planet," the old robot commented. "Never seen so much blue in one place before. Not since Blurr got himself blasted all over the landscape of Omicron Persei 8, anyway--"
Speechmaking and explanations followed, bringing the new arrivals up to speed for Earth. Introductions were made to the military humans already present, Lennox's team and the handful of F-22 pilots who had also helped. Sam and Mikaela arrived soon, having hung back out of the danger zone.
It was all very routine until Sam sneezed...