It's okay to be fooled by these 'animated' optical illusions. They totally look like they're moving. Hell, the cat watching them was fooled too. But the truth is, they're all just a masterful visual trick. The image isn't actually moving, the special sheet in front of it just makes it seem that way.
It's pretty cool. Brusspup, who has done similar tricks before, uses a transparent sheet with printed parallel lines on them and moves it across specific images to make it appear animated. The printed lines in the transparent sheet visually cuts the images perfectly to create movement.