In the pilot episode, Grissom takes over Warrick's investigation and goes to the house to collect toenail samples. The man says he already trimmed them and had tossed them in the toilet. Grissom asks to see the bathroom. The slip-up occurs when he enters the bathroom. At that time the toilet seat is already up, then he moves forward and it is down. You see him reach out and lift it, then the camera backs off and the seat is up.

Oops! : )