Was the mass in his mouth near his esophagus, or on his neck? The only hematoma's I've ever seen have been on horses and have resulted from being kicked or some other powerful blow. They're obviously on the outside of the obdy. If Jack's isn't on the outside of the body, I don't have a clue what would cause it, but I sure would want to know! Please let us know what you find out, and I hope Jack is feeling better soon.