Continuity mistake: In the scene where Annie and her children are getting in the car after church, she is wearing a dress but no sweater. When her friend comes over to tell her about Jessica's disappearance Annie is wearing a sweater over top of the dress. When she is turning to get in the car she is holding the sweater in her hand. Once she is in the car she is wearing the sweater again.
Continuity mistake: When Annie gets hit with the flashlight near the end, blood drips down very close to the crease of her eye. then after her friend saves her in the next scene the blood is farther away.
Continuity mistake: At the club when Katie Holmes is sitting with her fiancé, she is wearing a black strappy dress with a strap hanging off her shoulders. She stands up to go and dance with her father and in the next frame the strap is in place on her shoulder.
Continuity mistake: At the trial, the defence lawyer puts a dollar bill on the witness box while he is questioning Annie, which keeps moving, without anyone's help.
Answer: The TV in Annie's room.
The TV wasn't on before, and Annie is suspicious of the noise and light, which she wouldn't be if it was just the TV.