Flickr user Dan Bowles has made an interesting discovery you can try it out too. Turn off the lights in your room, Lift the mighty mouse and observe the light pattern created by the red LED underneath it forms the shape of a Mouse head. Jacqui Cheng of Arstechnica tried it out too "Skeptical, I waited until I got home from work to post about it so that I could observe this phenomenon with my very own Mighty Mouse and compare it to the optical patterns of other, non-mighty Apple mice. Indeed, my own Mighty Mouse produces this oddly creepy, mouse-like pattern just like in Mr. Bowles's pictures. I tested out a regular Apple optical mouse and saw a completely different light pattern, sort of like a four-way venn diagram. I even tried them both at different angles, hoping to prove that it was merely the light angle that was showing us our red, furry friend, but alas, that experiment was a failure. The two light patterns were definitely different."

Optical illusion or hardware easter egg you decide.
Via - Arstechnica and Dan Bowles (Flickr)