"You think I asked for this?" Stefan snaps at her, gesturing to Elena. "I'm sure she didn't, either. This won't break."

He grabs a handful of chain and shows it to her. The lack of a lock keeps him from saying that he can't break it, which is the big point here. Stefan could put his fist through the floor if he wanted to, but he can't break a flimsy little chain. Clever, hamsters. Very clever.