The artist, M.C. Escher, was fascinated by optical illusions.  
The waterfall is one example.

More Fun Stuff!

Illusions I
Illusions II
Weird Eyes I
Weird Eyes II
Weird Eyes III
Comics I
Comics II

The parts of the triangle puzzle have been moved around, but they are exactly the same size and shape in each puzzle. Print out the puzzle and cut out either puzzle.   Try moving the pieces around yourself.  It's mind boggling!  It's an illusion.  Study it carefully.

Say the COLOR of each word out loud.   It's hard isn't it!

The right side of your brain is trying to say the color while the left side is trying to read the word.