Continuity mistake: Fet is in the sewer looking for rats and encounters a group of infected. He is holding a handkerchief to his face with his left hand to mask the smell. He has his flashlight in his right hand, and pulls out an iron bar with his left. As the camera angle changes, his left hand is again covering his mouth with the handkerchief (no iron bar), then the angle changes again, and he's holding the iron bar again. (00:35:05)
The Saint of Last Resorts - S1-E8
Continuity mistake: John throws some stones onto a table to investigate whatever took the baby. The angle changes and they're in a completely different arrangement.
And They Were Enemies - S2-E10
Continuity mistake: The moment Madame Kali drops down dead, killed by werewolf Chandler, she's still wrinkled and old. Later on in that scene, though, when the monster runs off, her skin is all nice and smooth again. (00:19:10 - 00:20:05)