Noct and Prom both give off the energy that they bite during fights.
Noct only bites as a last resort, though. Like sometimes during training, when Gladio has him pinned, Noct just cronches down in a final attempt at winning. It pisses Gladio off so bad every time bc he never expects it. Definitely latches on like a leech and leaves a bruise in the perfect shape of his teeth. (Imagine a Tonberry taking him to court and suing, using the teeth imprint bruise as evidence. The Tonberry would win.) Probably bit Ardyn several times during the final fight just to prove a point tbh.
Prompto, though? Leaves no stone unbitten. He opens everything with his teeth, anyway. Why would fighting be different? Uses his chompers way more than he should and has chipped, and even broken a few before. (his dentist is a happy camper. Literally says, "See you next week!" before Prom leaves the office.) Dramatic, feral energy in a fight when it becomes close quarters bc he's not used to it. Runs at you, mouth open and teeth already clicking together like tap shoes on hardwood flooring. This boy isn't here to play. He will take a chunk out of a Cactuar. He does not care.