I bet if they really wanted to they could do some real damage.
When I hand feed mine shrimp, he sometimes grabs my finger by mistake (I think).
Shakes his head a few times and lets go. He draws blood everytime, and the sratches hurt for a few days.
Mine catches his pellets like a dog now, after months of trying to teach him, but he tagged me once and luckily my fingernail took the brunt. Didn't hurt , more scared me but after watching him strike when he's feeling sassy, I would be curious if you were going to dangle some fingers and tell us how bad it can hurt?
Once when I was dangling my hand over the tank my 20" aro jumped and grabed on and came out with my hand! So then I had to go about getting a STRONG 20" fish off of the ground and back into the tank! It hardly left a mark on my hand though, just really scared me! lol
I think this depends on how much grip the aro has, like how many teeth he actually used to sink in, cos often enough and aro will drop perfectly soft foods when they hit the water agian.
I think the real crunch is in the bony tongue?