In the comment section below, tell me which direction you see the woman spinning.... clockwise, or counter-clockwise? or both? This one really burnt my brain the first time I got it.
The fact is, she can be seen to be spinning in EITHER direction depending on how your brain is functioning. If you stare at the raised ankle when it's at 6 or 12 o'clock and try to force your mind to see it AS IF it were on the opposite side (so if it was at 6, you force yourself to see it as being at 12 and vice-versa) then you will see it as if it switched directions!
The relevance here is that, once you actually see the switch, and realize that it was "there" all along. You will get an even better understanding of just how well marketing, backed by billions of dollars of research, can take advantage of your mind.
In other words, they already know how you see things.
Here's a free pdf report titled, "The Battle for Your Mind"