The Latin verb illudere, meaning to deceive or mock, is the root of the English word illusion.
One of the simplest ways to detect how focused a person's brain is is to show them an optical illusion picture.
Researchers in the field of neuroscience have also studied the brain's reality perception using images of optical illusions.
Some research suggests that solving optical illusion puzzles on a regular basis can help people become more creative thinkers and problem solvers.
Above, you can see a herd of wildebeests frolicking through an African forest.
A zebra has managed to squeeze itself in among the herd of wildebeests.
Readers are challenged to identify the zebra within 8 seconds. Take this challenge to see how well you can see.