I once bit a pony I was schooling on the neck. He was a cranky little ba***d and kept turning to bite my legs. The second time he did I happened to be leaning forward and bit him on the neck. He never bit a rider under tack again.
I have a semi circle scar on my right index finger from being bitten. It is my own dumb fault. One day decided to check my mare's back teeth to see if she had any sharp points. I stick my hand in her mouth and start feeling around. DUH! She bit down and I almost lost the tip of my finger. Now, I do remember to grab the tongue when I want to poke around in the mouth.
My SO was bitten in the middle of his back while feeding his brother's horse. It was the morning he needed to report for his physical for the army. Everytime one of the Dr's looked at it, he needed to go through the explanation. When he got home that night he went out to the barn. He grab the horse on either side of the head and bit down on the horse's nose. My SO is not known to give up. Horse lifted him off his feet and shook him around trying to get rid of SO. Horse never bit after that.