Character mistake: Doc holds the binoculars the wrong way round. (00:30:20)
Other mistake: About 10 minutes in, Doc cocks his shotgun. Then he does it again, and no shellcase is ejected.
Revealing mistake: As the team is headed to Warren's hometown the show shows a clip of zombies in the field but it's the same 12 people (exact same outfits too) used in 11 different places in the exact same shot.
Revealing mistake: At the end of the episode when they show Citizen Z, the computer on his left has data or some kind of code running down the screen. Right after he puts his glasses on, the pause button appears mistakenly on the screen, revealing that it's not legitimately a program running, but just a video the effects team setup.
Continuity mistake: Right at the end, after Cassandra throws away the finger, there is the scene with her "family" finding the music box. Cutting back to her; she again has the finger resting on her shoulder/hair.
Continuity mistake: When the lieutenant and the new guy that joined up in season 2 are in the hospital, he reaches for his gun, shoots, and...click. No ammo. The lady then pulls our her gun, slide fully retracted, finger not on the trigger and states "yeah, me too." Thing is - if the slide was already retracted from running out of ammo - wouldn't she already know? I mean, she holstered the pistol. More egregiously, every shot before this, her slide was not retracted, and the pistol was ready to fire, until now, when she suddenly has a retracted slide.
Factual error: When the group are heading to California after leaving the Missouri home of Lt. Warren they somehow end up in South Dakota. And go within 251 miles of Salt Lake City and then back track over the Rocky mountains to the facility in Fort Collins Colorado.
Other mistake: Doc is walking through a field listening to the radio. In the sky, center of the screen, an airplane is seen for about 8 seconds.
The Siege of Murphytown - S3-E12
Continuity mistake: Towards the end a woman is walking towards the fence completely covered in blood and guts, we see close ups of her boots, trousers and hands all covered in dripping blood. In the next shot she is still walking but her boots and trousers are clean and the blood on her hands is very dry.
White Light - S2-E2
Continuity mistake: Roberta is checking her magazine on the pistol and it's empty. In the next scene, without reloading, she fires 3 more bullets. (00:29:10)
Revealing mistake: The lady that is with the other two guys that kidnapped Murphy decides to remove her magazine from her pistol. It's an airsoft pistol. The magazine has a front feeding area for 6mm BBs, and looks weird in general. She also has no ammo, as you can see the entirety of the internal spring - not bullets. And the magazine is weird too.
Die Zombie Die... Again - S1-E10
Revealing mistake: When Murphy gets back to the group after having walked about 10 miles with Amelia following who is now a walking Z, why doesn't she run past Murphy to the others?
Answer: When the plant zombies would attack they would wrap people with the vines and hold them, so they couldn't escape.