Hollow-Face illusion

The Hollow-Face illusion (also known as Hollow-Mask illusion) is an optical illusion in which the perception of a concave mask of a face appears as a normal convex face.

While a convex face will appear to look in a single direction, and a flat face such as the Lord Kitchener Wants You poster can appear to follow the moving viewer, a hollow face can appear to move its eyes faster than the viewer: looking forward when the viewer is directly ahead, but looking at an extreme angle when the viewer is only at a moderate angle.