You might not associate the mouth with fighting, except maybe to “slug them in the kisser”. But there are plenty of actions that a desperate person might do in combat using their oral cavity.
Here are a few suggestions for your maw:
Spitting is an Option
Spitting can be a taunt or a direct insult. On stage, we generally use a fake spit, especially if it’s aimed to the face. That dry spit takes practice to execute convincingly, so spend an appropriate amount of rehearsal time to get it right. Solicit opinions on your technique.
A staple of action movies is to spit blood after being punched in the mouth. If you load a bit of fake blood in the mouth, you can dribble it out the corner or spit it out onto the floor. If you’ve loaded it before the punch, you can spray blood as part of your reaction.
If that punch is big enough, you can load a Chicklet, Tic Tac or other small white candy, and spit out a tooth with the blood effect.
Perhaps the most tricky technique with the mouth is a believable bite, especially when the victim is struggling. Bites are obligatory in vampire movies, but also a natural reaction to someone trying to choke you or put their hand over your mouth to silence you.
It’s tricky because both operator and victim are in danger. The operator’s jaw is open, and therefore in a weak position, and may be dislocated. The victim’s skin may be ripped by sharp tooth edges, even without much pressure. Both sides must be careful.
We won’t go over the technique step-by-step here, but it’s part of the FDC certification course if you’re interested to learn it. I direct both actors to freeze during the bite for safety and to show the audience what’s happening. The pain reaction from the victim is screaming and drawing the body away while letting the operator control their arm.
I seldom insert things into actor’s mouths because it’s even more dangerous than the biting.
Fishhooking, as explained on Friends, is to pull an opponent with one or two fingers in their mouth. A bigger version happens with Jim Carrey’s bigger mouth in Ace Ventura: Pet Detective.
Dental torture was made famous in Marathon Man, and to a lesser extent in Little Shop of Horrors. Either way, you don’t have to show much to make the audience squirm.
Breathing Heavy and Screaming
Don’t save the explosive emissions for the end. Start your heavy breathing early in the process.
The most important tip for today is to really connect with your character’s stress in this life-or-death struggle. Even before the first blow is struck, if you can see violence coming, your system will flood with adrenaline and you’ll get tense and start breathing heavy. Then, as the fight truly progresses, you’ll marshall your strength by grunting. Depending on the severity, when you get hit you might groan or even scream.
It’s Valentine’s Day; you can give it more than lip-service.