ball in motion - sliding diagonally across a table top -
appears rolling, rising in the air, or bouncing, depending
on the relative position of its shadow (although the original
path of the ball remains unchanged!)
The green cylinder is placed on top or inside the polyhedron?
(see also kickboxer illusion)
"La scoperta dell'ombra" written by Roberto
is an excellent book about shadows...
We recommend it!