I love these clever visual illusion mind-blowers! I confess I keep playing the videos over and over and grinning at them every time!

Each uses the same trick – to make the box float or the eyes follow you –  the outside-in, concave version of a 3-D form.

Wondering if the phenomenon was first noticed when an artist or sculptor happened to glance back at the negative form from his or her positive casting.

The template here, provided by Rex Young, is a good way to try it out.