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.
Continuity mistake: When John is sitting on the couch eating cereal, the box of cereal disappears and then reappears.
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.
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.