Hey guys! It's Pikaboyx5 with a "under" theory! You can already tell by the pun that this is going to be about Sans! Also a other thing before we get started, I want you guys to comment questions or something about the theory, and this goes for all of my theories!
Remember Spoilers Ahead if you have not played the game! That is all which means that this theory starts now!
We all remember the Genocide Run of Undertale, where you kill everyone in the underground. Your last enemy of the game, the weakest character of them all, Sans. If you have played Undertale, you know that if you beat/kill Sans, he will start to bleed. Some have theories that this is ketchup.
I don't believe that, after all Sans doesn't turn into dust automatically when you beat him, like BOSS monsters, to not turn into dust you need a more stable body... A more "solid" body, that's why Sans is determined to kill you over and over again until you quit, and last time I checked determination melts monsters!
Which means that the "stuff" that he bleed wasn't ketchup... It was blood, a more stable matter for someone to stay alive! That's why he can stay alive when having so much determination. If you like this theory, leave a comment or favorite!
That's all for this time! This is Pikaboyx5, signing out! PEACE!