In my personal experience getting my jaw dislocated due trusting never have been something I concern. I absolutely agree that sucking a stallion is something that has to be done with care and lots of knowledge of behavior and physiology. But sometimes I wonder how many people do actually have experience with horses and aren't just saying fantastic scenarios they heard, made up or exaggerate their experience, I dare to say sometimes with the intention to shock newbies and get off that.
When you are sucking a stallion the first thing you will feel that can get seriously damaged due a sudden thrust (if you actually manage to reach this point which is hard) is your neck and the soft palate, lips can get injured to the point of bleeding by squishing them them against your teeth but its rare, at least only happened that to me once, got punched right on my lip when he trusted. Getting your neck injured definitely can happen quite easily but like almost always the biggest danger so far in my experience its not their penis (unless you put it in your ass) it is their hooves and weight. For example, another thing ive have heard that has some truth but find silly the way the danger is portrayed by some in an defunct forum; that their flare might dislocate your jaw tearing your face apart possibly killing you, and thus you should never let a stallion flare on your mouth. That's is partially true, their flare definitely can expand with enough force to possibly dislocate your jaw under ideal circumstances but again that's the least of your concerns, to go to the hospital with a injured masseter muscle.
The real issue is that once a stallion flares to any significant degree inside your mouth your skull can get locked up on their penis, if you try to get him out it might be too late or maybe not and injure him with your teeth as you pull him out, regardless of that the outcome will be very similar. At the same time this happens the stallion will freak out due pain because your teeth is biting into his very sensitive glans (and almost intermediately stop flaring but he wont deflate!) and certainly kick, that's were things get bad, you wont be able to really escape from under him if you get locked up, the chances of ending in the ER are very high because you got trampled or kicked. You wont feel the ache on your jaw because if you survive you will be pumped up with opioids to control the pain of your smashed bones, even worse, you will seriously injure the stallion's penis. So yeah, sucking a stallion almost like anything with horses is serious business, Im portraying worst case scenarios, It can be done with acceptable risk but that's up to you to decide, it has to be with care and never get crazy thinking you can handle him as if you sucked a human for a porn movie, that's an invitation to get your face smashed by a hoof, most importantly only do it when you have lots of experience with their behavior.
