Continuity mistake: When Daryl is driving the hospital van, it shows that he is going to land upside down, on the vehicle's roof, when he drives off the parking garage. In the next scene, the vehicle lands on its wheels, as if it has done a complete front flip. (00:30:00)
Continuity mistake: On the video of Ian supposedly killing Alison, we see her arm fall to the ground with her "Alison" bracelet visible. But in a later scene where Emily watches Ian put his bag in the athletics room, we cut back to the video and Alison's arm suddenly has a sleeve covering up her bracelet. When we see the video again later in the series, her bracelet is visible again.
Plot hole: In this episode all the students say Hollywood Arts has never had a prom before. But in the first episode, 'Pilot', Rex says to Cat after she runs out to tell Tori, Robbie, Andre and him that Sikowitz wants them to come back into the classroom, "Just like you wanted a date to the prom last year."
Continuity mistake: The Duncan family is forced to stay in a hotel while their termite devoured house is fixed. Dad draws up a sketch and is showing it to the family. When he brings his sketch in to show everyone, he is holding a black Sharpie, which then disappears and becomes a yellow mechanical pencil. Then the Sharpie returns for a bit, then changes back into a pencil again. (00:05:45)
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.
Visible crew/equipment: After Kristina explains the lunch problem to Adam, when Adam tells her that he's too busy to call the lunch vendor, in the next shot facing Kristina the T-mark can be seen taped to floor at the bottom, right side of the screen. (00:03:50)
Continuity mistake: In "Family Secrets" (episode 6) we learn Jimmy was lied to about being allergic to fruit (so he would not eat it all). So since he was a child he never ate fruit because he was told he was allergic to it. But in the season 1 finale there is a 5 year flash back where Jimmy is spending nights in the store dressed as "Drakkar Noir" he is eating apples and bananas - 5 years ago he still thought he was allergic to fruit.