Since the distance between the Zeeman sub-levels is a function of the magnetic field, this effect can be used to measure the magnetic field, e.g. that of the Sun and other stars or in laboratory plasmas.
Charley horse: Slang for a cramp in a muscle in the leg, usually caused by a strain or injury. A charley horse can last anywhere from a few seconds to over a quarter of an hour. It is not uncommon for one to recur before it finally resolves.
The only way to stop a charlie horse immediately is stretching the muscle to pull the knot out. For example, if you have a charlie horse in your calf muscle, reaching down, grabbing your toes, and pulling them forward, will pull the knot out of the calf muscle.