Revealing mistake: Any time any character is driving a Suburban, or any other vehicle with a column mounted shift lever, the shifter is in park while they appear to be driving.
Night of Desirable Objects - S2-E2
Revealing mistake: When the typewriter is being used at the end, the keys being pressed don't correspond to the words appearing on the paper. Obvious from the start - the first letter pressed is on the middle row of the keyboard, but the first word typed is "unacceptable".
Revealing mistake: When Connor and Cameron are trying to save Derek Reese from the police truck, Cameron walks on the Jeep's hood to jump onto the police truck. During her walk, we can see that it isn't Cameron but a stunt double. She doesn't look like Cameron and is a bit taller. (00:33:05)
Revealing mistake: In the morgue when Mike is just about to cover the first dead body, if you look closely you will see the body's eye move. (00:04:10)