I'm not sure I can explain it better. At the movies, you buy the tickets right there. You grab them and take them right to the ticket taker so you never "see" the end you hold. (In reality, you do for a second to take the tickets.) When you hand them to the taker, you expose the end you hold when you let go; ergo, you now "see" the "side" you never saw before.
Like I said, it's a bad joke.