I didn’t either. It just turned. Kind of reminds me of those posters that you had to stare at to see the picture that were popular for a little while.
The 3D ones? I love those. I can make the image in them pop out almost instantly.
http://www.magiceye.com/3dfun/stwkdisp.shtml
I finally got the cat to switch directions by gazing just to the left of it.