In the human brain we actually have tiny bar magnets or load stones in our cells as do many creatures that supposedly use it to navigate. From whales to bacteria it can be found (and some hypothesis the straight load stones found in some bacteria lead to the first back bones.) Yea, there are bacteria that use magnets to migrate too :P.

Anyways, the tai chi thing seems very different from your sister's experiment. They were in different buildings sometimes hundreds of feet apart and the apprentice would react when the master did his little DBZ shooty thingy with his hands :P (looked like it :P.) There may be some sort of coincidence but even if it happens 80-90% of the time I'd say there's something to it (just as long as they didn't you know, time the reactions for every minute or some shit like that :P.)

It's all being researched right now, anyways.