Continuity mistake: When Ted is captive and calls John on his iPhone, in one shot it's the right way up to his ear and then it's suddenly upside down.
Deliberate mistake: When Ted talks on his phone he places the phone in the position where a human ear would be located, yet Ted's ears are located on the top of his head.
Visible crew/equipment: In the scene where Flash punches through the wall and the neighbor stabs through with a knife, watch closely as the camera makes a mistake and films the "set." Basically what happens is the camera moves too far to the right and films for a split second the room the Asian neighbor is in, while you can still see the room Flash is in, revealing the studio built apartment.
Continuity mistake: When John & Lori are lying in bed talking (right before the thunderstorm), when you see John from his right side, his right arm is up and under his head. When you see him from Lori's side (his left), his right arm is down. The camera angles change frequently and his arm keeps switching depending on the angle.
Continuity mistake: When Ted is falling down, the bad guy pulls him with the left arm. In the next shot the bad guy is grabbing back with his right arm.