Revealing mistake: When Amanda and Fin are in Atlanta following up on their rape case, they walk past several cars with visible Georgia license plates mounted on the front. Georgia is a rear plate-only state and wouldn't have had license plates mounted on the front of the cars, as shown here. (00:13:30 - 00:16:20)
Revealing mistake: Near the end of the show where Liv elbows Stuckey you see a stunt double, then when he falls in a split second he's replaced with a dummy.
Revealing mistake: After M.E. Warner tells Fin and Munch the boy was smothered to death, you can see the foot of the "dead body" twitch or move.
Revealing mistake: After the detectives bust the cops while Undercover, Alex Cabot enters the interrogation room with Lorna Frankel. Shortly after, someone holding a white box is coming into view just outside the doorway. Benson is waiting for her cue to enter the room.
Birthright - S6-E1
Revealing mistake: When Munch is driving after the perpetrator you can see the dent in the side of the car moments before he actually hits the car and goes over the bonnet.