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.
A Charlie horse is when the muscle cramps up. It can be caused by a couple different vitamin shortages. Since your baby is taking all your nutrients, that's why they happen a lot during pregnancy, especially in your calves. Calcium, potassium, and magnesium are all ones I've heard that you need more of.