I did it in the second try... but i must say the animation is a trick. I followed carefully the ball, and after the first mixing of the cups the ball was not where it should be (the cup in the right). And it was only in the first mixing. All the next ones were done with the same level of attention, and all were correct.

Its impossible to choose the right one in the first attempt. I reloaded the page several times (to ensure i was making always the same test), and clicked at all the 3 cups, one each time. And never it was right. As the chance of being right is 1 in each 3, after several tries someone must suceed. But it was not so. Thats why i say its just a trick.

In this case, i just watch the woman, as it is FAR more entertaining than that idiotic cups...