We used to kill carp like that when we were kids. My mom bought me a bow fishing rig when I was 13 and it worked so much better and wasn't so primitive. here is a picture of a doe that liked to keep a dip in her mouth. She used to sleep on the door mat and she wasn't about to share her dip.
Your deer may of bit its tongue when it was exhausted and running or jumping. Ever seen a deer so wore out from being chased by something its tongue was hanging out. That would be a bad time to chomp down. I killed a deer with a bent face one time, always wondered what happened to it. Heres a picture of it, and a perfect example of an injury causing abnormal antler growth on the opposite side.