Learn this after you learn how to do two balls in one hand. This trick is almost just like the regular barbell trick. Instead of keeping one of the balls in your hand without ever throwing it, you throw it up and down, syncronized with a ball that you are juggling in the other hand (2 in one hand columns)
The "official" name of this trick may be wrong. Let me know if you know the correct name.
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... But if it's not, enjoy the video!