Lay a piece of thin paper over the monitor. Scroll down and trace the star below. Inside the star, trace and shade the smaller star. Use a pencil to draw the small star. Stand a mirror on the table and try to draw a line around the star by looking in the mirror. Does the pencil go where you want it to? Mirrors seem to change the directions; right, left, forwards and backwards; right?

Now put the drawing in front of the mirror. Put a stack of books in front of you so you can't see the drawing at all. Try to trace the path by looking in the mirror. In the mirror, all the directions have traded places!

Draw a big "69" on a piece of paper and put the paper on the wall. Now bend over and look at it between your legs. What do you see?

What happens if you turn the paper upside down and again bend over to look at it through your legs?

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Close your left eye. Hold up your index finger and line it up with a distant tree. Now open your left eye and close your right eye. What happens?

When you look out of your right eye, the tree appears to be lined up with the finger. But when you look out of your left eye, the tree seems to have moved to the left.

Each eye sees a thing at an angle that's a bit different from the other eye's view. This is how we see things as solid instead of flat.

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Roll up a piece of paper into a tube and hold it to your left eye. Look through it at the things in front of you. Now what happens when you look straight ahead? Remember to look straight ahead with both eyes open. Isn't that odd? It's as if you are looking through a hole in the palm of your hand!

What happens when: you close your right eye? you close your left eye? you move your palm up, down, forward and backward?

Because each eye sees a slightly different view, we can play these kind of optical illusion tricks.

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Stretch your arms in front of you and put your fingertips as you bring them closer to your eyes. What happens?

Your fingers look like sausages.

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Get a flashlight. Turn it on and whirl it around in the dark for your friends. What will they see?

They will see a circle because our eyes hold the light image for a while.

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Get a piece of cardboard and punch a hole through each end. Draw a goldfish on one side and a fishbowl on the other. Loop rubber bands through the holes. Then twist both of the rubber bands a bit. Next, pull on the ends of the rubber bands tightly. Now pull on the ends of the rubber bands so that they untwist and the pictures whirl. What do you see?

The goldfish is swimming in the bowl.

Our eyes hold a moving image a little bit longer than it takes for the image to move past.

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Cut a piece of cardboard in the shape of a triangle. Put a pencil tip or toothpick through the center. Now spin it. What do you see?

Now cut a piece of cardboard in the shape of a square. Put a toothpick or pencil tip through the center and spin it. What does the square look like as it spins?

We see a circle because our eyes hold the image of the corners as they spin around.