They’re cholla cactus also known as “jumping cholla” or “jumping cactus.” It has segments that detach easily and have nasty spines that aren’t easy to detach and are painful if they stick you. When someone tries to remove them from their clothes or shoes the pieces will often drop and stick to them elsewhere. It’s best to use a stick to kind of flick them away. It’s nasty stuff and people familiar with the Arizona desert know to stay away if at all possible.