I found this trick in the IJDb's JuggleWiki. From the title I guess it was probably discovered by playing around with the Juggleanim applet in the section's sandbox. This trick is a simple extension of The Follow.
Start off with all three balls & juggle Two in one hand in a rolling out pattern, while holding the third ball. Pick one of the balls in the two in one hand pattern, as you throw it carry the third ball held in the other hand in an arc that mirrors the path of the thrown ball, but on a larger scale. Think of two semicircles, one inside the other like a rainbow. The thrown ball follows the line of the inner circle & you carry the held ball along the line of the outer circle. Turn your carrying hand over from palm up to palm down during the carry. You should finish the carry at the same time as you catch the thrown ball. The move ends with you still juggling two in one hand, but with your arms crossed over.
Do the same again, but this time when the ball that your carrying hand follows reaches its peak, make the next two in one hand throw a bit higher than normal & throw it straight up in the centre of the pattern. As this ball peaks, throw the followed & carried balls simultaneously, in two parallel columns on the outside of the falling ball. Make the throws with your arms still crossed, the hand on the bottom throws normally, while the hand on top has to make a Claw throw. Catch & throw the falling ball with the hand on the bottom without uncrossing your arms. Throw it up on the inside of the two balls that were thrown simultaneously. At this point all three balls are in the air in three coloumns, two falling on the outside & one rising on the inside.
Now you have to do two things at the same time, the hand on the bottom uncrosses to catch the falling ball that was thrown by the hand on top. The hand on top uncrosses & Claw catches the falling ball in the middle of the three balls. Continue the clawing motion to drag the ball round the outside & underneath the rising ball. As the rising ball peaks make a rolling out two in one hand throw & continue juggling two in the opposite hand to the one you started with.
Now do the same on the other side. Practise this move switching from side to side. Once you are comfortable with the move on both sides it is time to tie the two together.
Perform the follow move exactly as before, carry a ball in an arc mirroring a ball in the two in one hand pattern, make the throw up in the centre of the pattern & then throw the two balls at the same time just as before. Catch & throw the single ball then claw catch the one falling in the middle & drag it down & underneath the single ball again as before. This time though, as you drag the clawed ball down, start to lead into the follow on the other side. Carry the ball held in the other hand (the one that was thrown claw-style) & follow the ball that you are dragging down as soon as it is thrown.
As usual, start off by just linking two sides together, performing the follow on one side then the other, then gradually work up to stringing more & more together.