"Seeing" things?

I was totally amazed but was wondering, if this is supposed to be a slide of hand type of illusion, why would there be a fade in and out when he takes the tile set out and then again when he was reversing the trick. If you look carefully at the middle of the tile field when he presses them together (after taking them out of the box) you'll see that the tile length is different. It's still an ingenious trick none the less.