Bird, lion, human — in any great portrait, you'll see that tiny dot of light that makes the subject look alive.

A dot of light from a red laser pointer may be thought to be due to a laser gunsight, causing outrage and possible danger.

They were then asked how much, in inches, the dot of light was moving.

In this experiment subjects were placed in a dark room and asked to look at a dot of light about 15 feet away.

It appears to move, and the participants are asked to estimate how far the dot of light moves.