Belly inflation is where one uses some pump mechanism to force air or water into his/her intestines. The pressure causes the intestines (and a little bit of the stomach, although this is not the...
many people do it, usually for sexual pleasure
yes, it will all gush out of your body soon after the inflation
If you want to inflate your belly big, you need a belt, tight tied on your chest, a bike pump or an aquarium compressor
Yes, if not done properly. If done correctly it is safe, Doctors use the method of inflation to have better access to the body during operations.