This actually happened to me in a hotel in Bali. It was night time and a light from the street was reflecting off of the mirror onto the wall. In front of the mirror was a statue of a goddess. Projected onto the wall were two separate shadows of the goddess, rotated with respect to one another about 90 degrees. I went to the mirror, stuck my arm into the light, and was able to have my two shadow arms appear to shake hands. How can this be?