“Papyrus pretends to be clueless in front of Sans to hide his true intelligence for mysterious reasons” or. and hear me out on this one. you gotta be dumb to set the joke up sometimes.
That’d be like saying my brother genuinely believes the random object he picked up is a telephone and that he can actually hear a voice on the other side ask for me. Except the joke is that I take the phone, and I go, “Uh huh, uh huh, okay….” and with a look of horror and shock I look at him and say, “They hit the second tower.” Sometimes he goes ahead and says the punchline himself. Still doesn’t mean it’s a real phone call to him.
Sometimes you gotta ask, “what’s updog?” You know the punchline. It’s just a routine for fun at this point. A reason to laugh in the middle of the day, because someone remembered the joke and wanted to share it.
Papyrus does lie and does say things that are suspicious but sometimes I see posts picking apart (what I think are) the wrong things, because they’re not considering the context as a whole. The game is funny. There are a lot of jokes all over the place. A character with depth will talk normal one second and then lose all braincells the next because their comedy partner showed up.
It’s good to think about and analyze because it’s a great mental exercise and will improve your overall reading and comprehension with future stories (games, books, etc). But sometimes, the answer to “why did he lie?” is “because he thought it’d be funny.”