Matt Pritchard. “Ambiguous Cardboard Arrows”. United Kingdom
The cut-up cardboard tube is a super simple design for creating an ambiguous object that can quickly and easily be constructed as a science craft project. Viewed from one angle it looks like an arrow pointing to the left. However, a rear view (or from a reflection in a mirror) has the arrow pointing in the opposite direction. When multiple objects are placed on the edge of a spinning turntable the observer can see the arrow magically morph from one state to the other. A variation has both the direction and colour of the arrow flip in a mirror.