Any submission, choke in particular where Jeff Monson has his bicep around your neck. Lots of different parts of your anatomy have a possibility of poping out. Just think of the possibilities.
Go without a coat when it's cold; find out what cold is. Go hungry; keep your existence lean. Wear away the fat, get down to the lean tissue and see what it's all about. The only time you define your character is when you go without. In times of hardship, you find out what you're made of and what you're capable of. If you're never tested, you'll never define you character.