Continuity mistake: In the scene where Scott is eating lunch and Allison comes and sits directly behind him, she sits down with a bottle of water and a bagged lunch. He has a tray lunch. Later on it the scene it changes: Allison has the tray lunch and he has the bagged lunch.
Continuity mistake: Erica is wearing a wedding band in the close-up of her hand on the rock wall. It doesn't show up in any other shot. (00:09:26)
Continuity mistake: While Stiles and Scott are at the vet getting the black dust, the vet puts the mountain ash on the table and says it's for Stiles. Stiles picks up the bottle and it's in his hand. A shot later the bottle of ash is back on the table, but Stiles never put it down. Then the shot after they show it on the table, it's back in Stiles' hand and he sets it back down.
Continuity mistake: Scott and Stiles are walking past a hallway and they see three dead policemen. At the beginning, the arms of the second policeman are lying on his legs. After the shot of Scott and Stiles, that policeman's arms are now by his side.
Continuity mistake: When Scott and Isaac are at the vet after helping Issac's dog, Isaac walks toward the door talking about the lacrosse game. If you look at Isaac's head, sometimes there is a tiny piece of hair sticking up and sometimes there isn't. It switches back and forth between shots.
Master Plan - S2-E13
Continuity mistake: In the scene where Stiles runs his jeep into the Kanima, he has no busted lip or bloody cheek, but moments later when the camera switches back to him, his injuries are once again visible. (00:30:10)