People have trouble finding the horse hidden in this ordinary image of a frog.
Visual games are a good way to exercise the brain. 
These “optical illusions” are proof that not everything we see is what it is. According to Susana Martinez-Conde, director of the visual neuroscience lab at the Barrow Neurological Institute in Phoenix, Arizona, “They are important tools for visual research, as they help us understand how visual processing works in the normal brain and in the diseased brain.”
“In other words, these games are not only a fun way to keep busy, but they’re also great for the mind.”
Yes, that’s a picture of a frog. But is there more to it than meets the eye? Take a good look.
What do you see in the picture – is the frog just sitting on the ground or on the edge of a pond?
Still don’t see the animal hiding in this photo of a frog?
Don’t worry, it’s not that simple! We forgive you if you haven’t managed to spot the other animal. Although the horse is hiding in plain sight, I had a little trouble at first too! Ready for the reveal?
Here’s the horse!
Look again at the image of the frog. This time it’s in plain sight.
Optical Illusion: People have trouble finding the horse hidden in this image