Wow, I wish I never clicked on this thread. Please, can an admin remove it or something? What's up with this pic?
It cuts off a little more of the person when it moves from 12 to 13 to make a new person... Notice the very top of the outer left persons head is left as a buzz cut, then a little more and a little more till at 13 they have a new person... This is just imo i didn't watch it to long to check my theory.
12 or 13 is not a question but I admit the idea behind moving a intellectually selected piece of drawing right to left and vice-versa is unique. One disadvantage with this gif animation is the trick can't be noticed until unless it was told.
I counted 13, concentrate on a certain part of them such as the shoes or eyes, ignore the rest as it'll confuse you.