Papyrus' ears go back at the reminder of the fleetingness of everything. One of the things about bones is how they last. They're used a metaphors for permanence in human art and literature because they're the last to decay, which is quite the flattery to a living skeleton.

But it really is strange how that feels, for ears to fold back like that, and he raises a paw to rub at them while Joker starts mulling things over.

"If the idea is something besides laughing at your own jokes, I've done my job." Papyrus says with an emphatic nod as emphasis, since he can't rest a hand on his hip and look all cool now. Then he tilts his head at Joker. "So, what kind of idea? If you want to share."