Learn this after you learn how to do two balls in one hand. With this trick, you switch off from each hand doing 2 in each hand. Throw one ball straight up from the hand with 2 balls in it, and let it fall straight down into the same hand. Right before you catch it, throw the other ball from that hand straight up. Instead of catching the second ball with the same hand, first throw up the ball in the opposite hand that you threw the one that you need to catch, and then catch the ball that switched hands. You still have the ball that you threw to catch that ball in the air, and it acts just like the first throw of this trick. It falls back to the same hand, and you throw up the other ball and catch it with your opposite hand. And continue the pattern, back and forth, and you're done.
Confused? I'm sure I would be if I wasn't writing this. Watch the video to clear up how you do this trick. It should work, unless too many people are watching it at once. If that's the case the whole site should shut down soon... Enjoy it.
