Well, there was the bit about alternate universes. Apparently sometimes people show up that are -- basically the same as someone already here. Reid explained it like this: every time we make a decision, we're making a new alternate branch of a universe. So if I decide to go to the coffee shop before work, there's another universe out there that's different from mine because that Garcia didn't have a jonesing for a latte.
...Only Reid wanted to say that using a dead cat in a box or something. Totally morbid. I much prefer the latte analogy.