This question already has an answer here:
Here is a GIF image illustrating a supposedly "infinite" supply of white chocolate.
After watching this repeatedly, I can't definitively say why it doesn't add up. It clearly can't be infinite and the sizes of the pieces don't seem to be changed/edited. My guess is that the volume of the spaces between pieces somehow adds up to the final piece's volume.
However, the real question I have is: how have the dimensions of the array of chocolate changed? That is, if you start with a $6\times 4$ grid of chocolate pips, what are the final dimensions of the almost complete grid? I figure that height need not be considered because the cuts are made normal to the table surface.