Did the narration say don't touch the skeleton? Well, he sure doesn't hear it. Papyrus kneels next to the totally-sleeping decoration and rests a hand on its shoulder.

"I'm offering assistance," he calls over. "It seems someone has fallen asleep on your lawn!" The alternative is that they've fallen down here, and then someone put a sword in them for mysterious reasons? Or that the sword is part of that. Now that would be strange.