A remarkable number of people are familiar with a joint that you really have no business knowing about unless you're an anatomy professor.
It's not like your elbow or knee or wrist that you willingly use every day. In fact, it barely even moves at all, but rather wiggles a little when you walk in a tiny figure 8 pattern that is virtually undetectable to all but the trained professional's eye.
t's called your Sacroiliac Joint or SI joint, and if you put your hands on your hips backwards, your fingers would pretty much be right on top of the joint. Not exactly one of the "head, shoulders, knees, and toes" parts of the body we refer to on a regular basis.