The boards on the windows and the junk outside the depot appear and disappear between shots.
When Melanie is having lunch at school, as the shot switches back and forth between her and the boy, her right bra strap keeps switching positions.
When Melanie receives the text message from her sister you can see the cursor blinking, showing that she is actually writing the text message, not receiving it.
When the parents cut Melanie's hair to get it tested for recent drug use, they only cut some off the end. The most recent traces would be near the scalp.