Continuity mistake: When Scott runs into his room after the party the shadow of the blinds can be seen all the way across the room, but in the next shot of the window, the blinds are only halfway down. The shadows cast doesn't match.
Continuity mistake: When Scott loses his asthma inhaler, we see it fly out of his hand and land on the ground and it is a light khaki colour. Later on, when Scott and Stiles go back to the woods in the day to look for the inhaler, they come across Derek and when Derek throws Scott his inhaler, it is a white colour.
Second Chance at First Line - S1-E2
Continuity mistake: When Allison opens her locker, the things inside change from shot to shot.
Continuity mistake: When Derek finds the note on his car it's snowing, in the next shot it's not.
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)
Continuity mistake: Scott and Kira are having dinner with her parents. In one shot, Scott picks up sushi with chopsticks. In the next shot, the chopsticks hold nothing. (00:27:30)
Continuity mistake: Scott becomes more monstrous due to his new Alpha status. He even says that he now has extra fangs but later in the series, these fangs are gone with no real explanation to what happened to them.
Continuity mistake: The McCall house has its electricity shut off but at the end of the episode Scott's bedside lamp still works.
