1. Imagine this picture as a pup tent made of clear plastic. Which side looks like it's in front, and which side looks like it's in back?  
 

2. Can you mentally "flip" the picture, so that you see what used to be the front side as being in back?
3. If you're having trouble getting it to work, take a look at the pictures below. We've shaded one side of the pup tent so that you can see two different views. Look at the two views, then look back at the clear tent above. Can you "flip" the picture from one view to the other?

4. Now take a look at this picture. Imagine that it's a box made of clear plastic. Find the small star in the upper left corner of one of the cube's faces. Does the face with the star look like it's up front, or in the back? Can you get it to switch?	5. Practice flipping back and forth between the two views. How long does it take to switch each time? The more you do it, the easier it gets.

Now try just staring at the cube. Notice which face is in front, but don't try to change it. Stare at it for a minute or so. Chances are, the cube will flip back and forth all by itself!

Psychologists have two theories about why pictures like these flip back and forth. The first that it depends on which part of the picture you're looking at. Shifting your gaze from one part of the picture to another may make the picture flip.

The other theory is that your brain gets tired of looking at it one way and switches to the other to give itself a break.