I studied this rug in depth yesterday and it only became more beautiful the longer I looked. Noticing the many nuances of it's detailed drawing I did find the intentional mistake. In fact, I found two. My hint is that the rug is not exactly the same from left to right, nor top to bottom yet perfectly balanced in color and design. That takes skill. To find the intentional mistakes, you may have to come and see this wonderful work of art in person. You are invited!
This piece is 10'3 x 13'9".