Sans looks at Papyrus, sort of baffled for a moment. Then, his grin cautiously widens. Papyrus has always been blessed with the ability to misinterpret just about anything.

"It was shapeshifting," he clarifies, with the vaguely academic tone he gets when he legitimately tries to explain something, usually in small doses. "It's just that it takes a lot more dust to make a monster that big, instead of a monster this big." He gestures at his diminutive self. "So, when I don't have enough magic to maintain it anymore..."

He shrugs a shoulder.

"What's left over turns to dust, and what isn't turns back into me."