I have TMJ (temporomandibular joint) syndrome in my left jaw, so gags do tend to hurt me in a short period of time. The same can be said of giving oral sex and chewing gum or tough meat. Bondage in and of itself doesn't hurt. Nothing should be tied so tight that it hurts because lack of circulation can cause tissue damage that is sometimes permanent, such as damage to the radial nerve in your wrist, leading to tingling and numbness in the affected limb. If using rope, it should be tied in such a way as to allow quick removal in case of a problem, like a clove hitch or similar knot. Leather restraints that are padded are a good choice. My wrists are so tiny that those have to be buckled in the last hole in order to keep me from pulling out of them, but they don't cut off the circulation.