For each step he takes back, Mirabel takes a step forward. He wasn't able to escape her when she demanded a vision from him, and she doesn't plan on letting him escape now.

"Tio, your hands are bleeding. Let go of it!"

She hasn't seen the tiny mouths on the case and therefore doesn't know that's why he's bleeding, but it doesn't matter. She pauses, and in an act of Mirabel Bad Decisions (TM), she makes a grab for his wrist.