"Looks human enough that even humans will trust them..."

"If they just look human... and everyone found out they weren't... The humans might feel surprised, betrayed! It could go badly. We'd have to get a real human to do it."

"Well, that's easy! We're already friends with a human." Papyrus's jaw shifts a little to the side, like a slight grimace. "But... in all fairness, they killed a few monsters. We'll have to convince them to do better, when we go back!"