I use small 1/0 or smaller hooks, if they can fit it in their mouth at all they will swallow it. The trick is keeping a tight line and setting the hook on the slightest of bites. You may miss a lot of fish setting the hook early, but aren't shy they will come right back lol. Its best to have a good tool for hook removal when targeting them. Its pretty funny though to take a new fisherman fishing for bullhead, hold the fish for them and make them stick their finger in its mouth to get the hook! I've done it to several people over the years and they are always shocked at how hard those little buggers can clamp down, its always hilarious. I swear if those things got as big as flathead or blues, they would crush your hand... lol