Ladies and gentlemen, I'm not a Toastmaster—I'm more of an Osterizer, actually—and I don't memorize my speeches, so you'll forgive the occasional reference I make to my notes. I promise you it won't be as painful as this handful of paper may indicate.

On the other hand, how did it turn out last time a dentist told you it won't hurt a bit?

Human beings have two eyes aimed in roughly the same direction because each offers a slightly differing view of the world. The contrasting images they produce, superimposed in a portion of the brain called the thalamus, give us an "in-depth" picture of our environment containing more information than would both viewpoints considered separately. We call such a picture "three dimensional", and the physical phenomenon which makes it possible is called "parallax".

For the same reason, we have two ears to tell us not just the direction noise comes from, but how far away the source is. Parallax informs us which way the train is coming from, where the woodwinds are relative to the brass, and who's the better guitar soloist in the Eagles' historic live performance of "Hotel California".