A severed tongue is the tongue of a person or animal that has been forcibly removed. This actually happens more often than one would think. The practice of severing one's tongue dates all the way back to Ancient Egypt. When a person was being punished for some blasphemous act, they would often be mummified while still alive. Part of this process involved the removal of the tongue so that the voice of the victim would not offend the Gods.
In the 1987 film A Nightmare on Elm Street 3: Dream Warriors, a teenager named Joey Crusel had a nightmare in which a hot nurse named Marcie pinned him to a bed and bound his hands and feet with projectile tongues. No, I'm not making this up. If you haven't seen the movie, believe me... it happens!