This is also one of my favorite things. I cum much, much harder when asphyxiating for some reason. Sometimes, it's with his hands around my neck, which is just okay for me as it won't induce me to cum any harder or faster since you can't really cut off all air that way without risking damage to the delicate tissues in the neck. Usually, it's with his cock in my throat, either holding my head while he forces his cock into my throat or in a 69 position with him on top (my favorite). I just push his hips to let him know when I need to breathe again. I also really love a pillow over my face which is hard to get anyone to do since they can't really tell what's going on under the pillow. Occasionally, I'll put my own face into a pillow while being fucked from behind. I learned to do it quite by accident while masturbating. I'd put a pillow over my face to muffle the sounds I was making while cumming and noticed it felt so much better. I've been doing that for years. The more I need to breathe, the more aroused I become while having my clitoris stimulated (since I'm a clitoral orgasmer). Orgasm is reached at about the same time I feel my body begin to struggle from lack of air. I know many people consider this particular activity too dangerous, but I feel that if proper precautions are taken to minimize the risk, it's not any more dangerous than holding your breath for as long as you can. Never wrap anything around your head or neck, such as a belt or plastic bag, while alone. Common sense should tell you that. I don't prefer the choking sensation of something around my neck anyway, but if you do, care should be taken because it's also the most dangerous. It can cut off the blood supply to your brain and cause permanent damage in either the brain or neck. I also don't recommend continuing until passing out as it only takes about 5 minutes for anoxic brain damage to occur. Passing out from lack of oxygen can induce a heart attack or seizure leading to a permanent vegetative state or even death.