In the scene where Alan is giving the seminar, he is talking into a microphone that is attached to the podium. Well, if you look at the bottom of the microphone, there is a spot for a plug in, but yet there isn't one, and the microphone still works. Not very exciting, but a slip-up no less.
Jurrasic Park III
I was hoping to challenge the slip up submitted. I see a few others already knew the correct answer. I work for an AV Company and it is easier to just put the cord less microphone on the stand or podium in case the main speaker wants to move it... the red light on the bottom of the wireless microphone is the battery indicator =)