Nice work.
That horse doesn't have a mouth at all if you can't stop him with that bit.
He's always had a really good mouth and would stop with just a bump on the reins or a squeeze of your legs. But between my kids and my friends kids he has gotten away with a lot that he shouldn't. He just needs a reminder of what whoa means. It'll make him stop or pass out and an unconscious horse can't run off with you !