Mrs Weasley did not seem entirely satisfied with Mr Weasley's answer. As her husband leaned over to shake Harry's hand, she peered at the bandaging under his nightshirt.
"Arthur," she said, with a snap in her voice like a mousetrap, "you've had your bandages changed. ..."
Harry Potter and the Order of the Phoenix
I don't quite get the idea of "with a snap in her voice like a mousetrap" in this context. How should we understand it?