>>2242189>no longer have fleshWhy are you in this thread if you don't know anything about the game.
The skeletons aren't dead; they're alive. They are creatures that just so happen to be shaped like human skeletons, but they are not, in fact, biologically human. They eat, breathe, sleep, cry tears, sweat, feel pain, same as anyone else.
Monsters in Undertale canonly have the power to magic-up physical objects from thin air. It's not too far a stretch to suggest they'd use that natural ability for sexual purposes.