If you look not closely enough you’ll see
something else among this image.
(Click to enlarge)
I found this at the HospiceCare and Share Thrift in Boulder. The instructions:
Hold this postcard right up to your nose and very very slowly pull it away from your face. Look through the image without focusing on it. Try not to blink, and a hidden image will magically appear!
Hidden Image: Trapeze performers
Making our eyes visually fooled is another good way to exercise them as what my local optician told me.