Even if my threshold of pain is very low, I've noticed that I rarely tend to scream or cry out because of physical pain. I cry because of emotional anguish every other day, but I cry much less over wounds, especially in recent years. For example, the pain on my hand because of the burn was horrible, and it was augmented greatly when I was in the shower, because warm water kept splashing onto it. But I didn't cry, or even shriek, or even say something like 'Goddammit ow!' :3;

I don't scream on roller coasters either, which may be a bad thing, because I read that screaming is supposed to release the air pressure your body builds up from moving so fast...