"Nah, I didn't write a letter." At least, that's the lie Sans is going to tell Papyrus, so it's easier if he just tells everyone the same thing. Never mind that the gift he got from Santa, now addressed to Papyrus, is also in his paper bag. "I'm guessin' that's not exactly what you were expecting?"

Sans checked his own before carefully rewrapping it, and while racecar slippers are sort of similar, they're not exactly a racecar bed.