Who know? Where's the trick?

As all of us (my friends and I in RMIT-Informatics) have tried to find out where the hole come from, but we could not do so. Even, one of my friends has the picture printed, and cut it to 4 parts by its color, and then join it by 2 ways as shown in the picture... But he could not find out why, either.

Yes, the question is "HOW CAN THIS BE TRUE?". Can some1 pls try and find out why?

P.S: ASAP