It's the sceen where Jack Traven is racing on the high way to catch the Bus 2525 to warn them of the bomb. In the sceen, he's slamming his hand on a bar on the steering column which is attched to the horn. It's white and looks like a wheel within a wheel. After the camera cuts to the next sceen then back at Jack driving...the horn's gone. Not only to they show it there, but they show the shot without the horn 2 more times. I thought it was neat.