When Beth has her picture hanging up inside Adam's closet, he turns around to look at her and the clock next to Beth says 10:40. Then Adam looks at the picture again in confusion then looks at Beth again a few seconds later and the clock next to Beth then reads 10:39.
When Adam is using his laptop at home, the "PowerBook G4" logo is visible below the screen. Two shots later, the logo has been painted out.
When Adam is sitting on the steps of the apartment and Beth comes back out to talk to him the door behind her changes from slightly open to closed.
When Beth is talking on the phone inside the classroom, the motion of the woman in the background is reversed.
In response to Beth's query about what "10 to the minus 39th power" means, Adam states that it is the number represented by a decimal point followed by 39 zeros followed by a "1". Actually, it is the number represented by a decimal point followed by 38 zeros followed by a "1".