He hid himself in a room full of nothing but spaghetti made by Papyrus! The only way to find him and be sure of his destruction... is to eat all of it!
You eat the spaghetti, you are filled with nausea but manage to go on despite that your body tells you to stop. Sans is horrified by this insane self torture as Papyrus smiles filled with joy for your passion towards his spaghetti. You finally find the tomato, you stare at each other, determined, you leap at the tomato and.... Give it a careful pet! Undyne frowns at your shinenigans.