The laps shutter of 2 seconds allows your talent or subject to make quick and abrupt movements that will superimpose the secondary image over the original image. Here the model holds a plastic skull in front of their face, counts one second and quickly removes the plastic skull allowing the facial image to peek through. The end result is a nearly X-Ray effect over the models head. Granted you could photoshop this trick, but it is far more challenging to attempt it in the camera. This was take # 15 or 16.