* The name.
** It's a ''primer'' (information given to bring one up to date on what's happening).
** And [[http://en.wikipedia.org/wiki/Prime_%28symbol%29 prime]] is also used in physics for when a variable changes slightly. Not only does the box send them to a slightly different time, but it's also a slightly different 'them'.
** "Prime" also means "first." Once Abe and Aaron begin working at cross purposes, each is trying to travel back further to get the edge on the other; each is trying to be primer. Their names reflect this too: both are names that can be reasonably expected to be first in an alphabetic list. But as long as it's spelled that way, "Aaron" will always come first.
** Primer also being the firing mechanism in an explosive that sets off the chain reaction of events to create the rest of the explosion.
** The time machine must literally be primed before each use.
* One of the major themes of the movie is discoveries often being accidental and unceremonious; the creators mention penicillin as an example of such a major and accidental discovery. Abe and Aaron discover they have a time travel device via a weird pattern of fungus growth, which parallels the discovery of penicillin.
* The scene where Abe and Aaron discover they've had the same dream seems like a throwaway moment at first, but if you think about it for a second on a rewatch you realize that [[spoiler: Abe told Aaron about his dream on the first go-through and repeat Aaron is just messing with him]].

FridgeLogic: [[Headscratchers/{{Primer}} Here]].