The double shadow

To create two shadows with only one light source we need an additional tool:

By using a mirror, Professor Threestone can create two shadows with only one light source. Usually, only two shadows are created behind an object when there are two sources of light. It is the same in this case. The mirror "doubles" the light source. The reflexion of the source, the virtual source, also creates a shadow, just like a real one. How can that be explained? The mirror reflects the light of the real light source so that the object is illuminated from two sides. Therefore, two shadows are created. However, for us is seems as if there was a second source of light behind the mirror.