First time we did my newer mare's teeth we discovered a horrible ragged scar on her tongue. The vet said it looked like someone had put a chain on her tongue (a nasty way to restrain a horse). She is so gentle and smart, I have no idea what kind of situation would have required such an overkill kind of treatment. Maybe related to the rope-burns or wire cuts on her legs? It doesn't seem to bother her - she has always taken the bit from our hands, and worked fine in a bit. She's fine about her legs being handled, too. Whatever happened must have only happened one time, and she's forgotten it.