When Spencer and Emily are in Spencer's kitchen talking Spencer stacks their plates but when Emily is leaving the plates aren't stacked anymore.
When Hanna and Caleb are talking about him sabotaging Mrs. Montgomery's car, the sticker on the inside of Hanna's locker (above the picture of her and Mona) is crooked on the far away shots and straight on the close ups.
When Aria and Emily walk up on Hanna on the phone with her mom, in the school hallway, pictures and stickers can be seen on the inside of Hanna's locker door, when the camera show all the Liars, the pictures and stickers are gone.
In the scene when Ezra rides up behind Aria in the Limo, his hand is up to his head, as if he is on the phone. The camera then cuts to Ezra in the Limo and you see him answer his phone.
When Caleb and Hanna are in detention and are talking, when the screen is on Hanna there is hair in front of her ear but when the screen is in on Caleb the hairs are tucked behind her ear.