When Lydia is facing down the altered Jackson, she holds up a key in her hand to show that she knows his mind is still in there. When the camera is behind her there is about 2 inches of the key showing. But when the camera changes to her front only about an inch of the key is showing.
After Stiles gets home from getting beat up by Gerard you can see the makeup used to create the bruise when he gets up from his bed to open the door when Lydia knocks.
When Stiles brings Lydia toilet paper when she is crying and says that he doesn't have any tissues, there is a box of tissues visible in the shelf behind them.