Interesting puzzle

This was an interesting forward sent by one of my friends. The total number of people in the GIF image changes when the transition occurs. The explanation is quite complex and basically deals with the way humans percieve visual inputs. Unfortunately I deleted the mail containing the link to the explanation, will post the explanation when I get my hands on it.

Exams are on and right now life is quite bleak with occasional silver linings like this break.

So long till the next post.