I've seen people react so instinctively to tap-out signals both in martial arts and sometimes outside of it that I've often wondered if you could fight dirty in a real fight by tapping out and then clocking them or at least breaking a hold during that instant where they start to back off.

I think I have used it successfully both in chiropractic and physical therapy contexts. The thing with really top-shelf pain is that if you're not screaming you can't even talk at all. But your hands still work.

These sorts of little reflexive physical communications are super effective.