You were taken in by Sans and Papyrus when you fell into the underground. Right now, Papyrus was out training with Undyne and even though Sans was meant to be at his station he's at home taking care of you. But it's more like you're taking care of him since he's sleeping on the couch right now with you doing your thing.

CCRRRKKK

You accidentally made a loud noise, waking up Sans and putting him in a groggy state.

"Ughh... Kiddo, what was that?"