Re: SGU question
I can't point you to a specific episode but the crystals were introduced in SGI in a two or three episode story arc.
As I recall that while the remotes exchange bodies with the local they see themselves in a mirror. The main problem with SGU is that I haven't learned the characters well enough to know who is who. I got it with the colonel exchange but was somewhat confused by the others. I expect we will see a lot of swapping out between the colonels because of the differing skill sets and the star quality of the two actors.