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Ready to test your concentration powers and cognitive flexibility? Try this classic brain teaser, fun for kids and adults alike.
Quick! Say aloud what color you see in every word. Don’t read the word — say the color 
Tougher than expected, right? This brain teaser is actually called the Stroop Test and is often used in neuropsychological evaluations to measure executive functions such as cognitive flexibility, inhibition and self-regulation capability.
For more brain teasers and also visual illusions:
You say you can count? Check out this brief attention experiment