Few knew about the device beneath the Skeleton brothers’ house.
For a gloriously convenient (if short) while, the only one who knew had been Sans, and Sans alone, recovering the parts of the failed experiment from where they had been blown apart. He did what he could to get it to the point of resembling something remotely salvageable, but after that he got overwhelmed and gave up on it. Tossed a sheet on top; called it a day.
Then, it was Sans who knew, and Papyrus who sort of knew but didn't really know, having discovered it while cleaning, later asking about it in the way he always seemed to resort to: mentioning “SANS’S STRANGE AND MYSTERIOUS SCIENCE MACHINE UNDER THE HOUSE” loudly and incessantly in conversation with others in earshot of Sans until Sans caved enough to give him a vague acknowledgement and an ironically fitting yet dismissive joke that Papyrus could mull over, like his horoscope or a junior jumble.
And then it was Sans who knew, Papyrus who likely guessed, and Undyne who overheard, when Papyrus decided he needed a confirmation and loudly announced when the two were watching some Mettaton show on the couch that Sans had a similar “STRANGE PORTAL TO THE MOON OR SOMETHING BENEATH THE STAIRS” and Sans winked and called “it out of this world,” while dying and screaming on the inside.
Then it was Sans who knew, Papyrus who guessed, Undyne who thought it was imaginary, and Alphys who heard Undyne mention it and started watching on the surveillance for Sans's comings and goings with parts too bulky to fit under his hoodie or inside his pockets, not walking past certain cameras after waltzing in front of others. She called him up, (that alone showing she meant business) ranting about his not asking her to get involved. He shot her down with a joke that may have been just the slightest touch too harsh, and he regretted it.
Then it was Sans who knew, Papyrus who "knew”, Undyne who heard of it, Alphys who was mad about it, and Mettaton who overheard the screaming between his friends and a mysterious stranger on the phone about “the interdimensionality device” and thought the name was so genuine and scientific, he just had to use it in one of his terrible screenplays.
Then it was Sans who knew, Papyrus who also knew, Undyne who didn't know, Alphys who knew and was vagueblogging about it, Mettaton who made a movie about it, 73% of the 13-to-301 demographic who watched a movie based on a true story about it… and 7 animation-enthusiast forum-goers who were aware that “[The Anonymous Anime Lizard’s] ex-best-friend didnt even text [them] about the old project and had the audacity to joke about it after not even saying hey for 5 months and what the hell sa– sam– sasam, [TAAL] was the one who suggested [TAAL and Sasam, together] try to pick up where [they] left off!!!! and then he throws what happened 5 years ago in [TAAL’s] face!!!!!!!! (╬ಠ益ಠ)”
Then it was Sans, Alphys, and Papyrus who knew, Undyne who was starting to realize, Mettaton who was making a sequel, 92% of the estimated population of the underground who had seen a movie about it, most of the undernet who had seen a post about it, and a little old lady who lives in the Ruins, who Sans vented to about how everyone knows about his dumb project and no one will just chill and let him work on it. She gave him a recipe for a poor, to cheer him up. It didn't work even if it was really good.
Then it was Sans, Alphys, Papyrus, Undyne, the old woman, Mettaton, 94% of the estimated population of the underground, and the King who knew, though how much the king understood, Sans couldn't tell ya. He was used to giving vague, cryptic answers, but this was the king, so he resolved himself to honesty for once in his life, when the monarch gave him that sad, kind smile and asked if his “big science project from the television programs” could really break the barrier like all those nice monsters had been asking him about. But Asgore didn't know how to work a VCR, let alone how to understand a multidimensional transport device that didn't work and could probably erase people from the fabric of reality (and probably did that before if it ever got to working in the first place, but that wasn't something Sans liked to think about, so he just straight-up didn't). It didn't matter what he understood. Sans got named Co-Royal-Scientist and forced to do an actual job, with Alphys, who was still a little mad at him, and suddenly very cagey about letting him into the labs.
Few knew about the device beneath the Skeleton brothers’ house.
Few knew about the device beneath the Skeleton brothers’ house, only everyone that Sans had ever met in his entire life…
…and many other monsters he hadn't had the pleasure of meeting yet, including the Prince of All Monsters, who was apparently a tiny yellow flower that Asgore hadn't told anyone about, somehow being a better secret keeper than Sans, who used to think he knew a thing or two about keeping awesome secrets. But yeah, go figure. A Flower Prince, which was weird, but whatever, Sans was 110% done. Everyone knew about his secret non-functional device. Might as well fill an undead miniature monarch in on all the big news, right? Fantastic. Great. He was doomed to work on a project that wouldn't be finished, forever. Life was pointless, so sure, tiny flower Prince wants to see some melted hunks of metal? He's not gonna stop him. Sure. See? See, kid? Isn't it so impressive how it's all congealed and nothing works and he would be so much further if people would just drop the subject and let him do things his way? Is this what you wanted to see, kid!? Because Sans is the most laid back, chill guy in the underground (really!) and he's actually, like, genuinely a decent scientist? But all he wanted was to keep one thing a secret, one tiny little thing, a hobby, a side project , a long shot that wouldn't ever work, and this is what he gets. He's having a meltdown in front of a magical reanimated photosynthesis baby (“Hey! I'm not a baby!!!”) and everything is terrible and all he wants is a little bit of privacy. Does the prince want to know his birth date? How about the last four numbers of his social? Bank account info? Private telephone number?? Greatest fear??? Most embarrassing memory??? What else does this world want from him??? Hell, kid, if someone could magically go back in time and stop everyone from finding out about this and most of all finding out what a freaking mess he actually is then he would be in their debt foreve——
Few knew about the device beneath the Skeleton brothers’ house. It was just Sans.
Or… at least it should have been, but then there was this kid… plant… thing at his doorstep with a big wide grin, saying that he owed him one, and rambling on about what a big, good helper he was, and something about a life debt. And it was real cute but Sans had no idea how this kid could know what he knew.
Shrugging, Sans asked the kid to keep it a secret because he felt very strongly that his life would be exponentially worse off if even a single other person besides the two of them knew about it.
“Oh you have no idea, mister!”