When the girls are watching the Alison video at the beginning of episode you see Ali's bracelet when she hits the dirt. Later at 16:49 Ian and Spencer are talking about her laptop and the dance, Spencer has a flashback of Alison's arm hitting the dirt from the video, this time Alison's bracelet is covered.
When the girls are watching the Allison video, there is a play button showing on the screen. If a video was playing, the spot where the play button is should show a pause button.
When Hanna is trying to leave and Lucas asks if he can drive her home, she calls him Ian instead of Lucas.