Naked Gun 2&1/2, The smell of fear - Blank Sketchpad
Go to the scene whereFrank first sees Jane after the explosion near the start.
When Ed is looking at the sketch pad that the sketch artist drew a picture of Jane, he flips the pages fast and reveals a weird picture for the camera. If you look when he is flipping, you notice the page he was looking at was blank, both times he flips the pages