I like this trick, partly because I came up with it myself & partly because it links really nicely into any other trick that involves an orbit. This trick is very closely related to The Follow.
Hold one ball in each hand one above the other about six inches apart in the centre of the body. Imagine a small circle between the two balls where the upper ball is on the top edge & the lower ball is on the bottom.
Start by carrying the balls around the circle. If your left hand is on top circle in an anticlockwise direction & if your right hand is on top circle in a clockwise direction. Keep your hands really tight together. When the hand that was on top passes underneath the other throw the ball Under the arm so that it goes over your other arm & will land in the centre of the pattern. Continue the carry with the other arm in an orbit around the thrown ball. When your carrying hand has circled round to a point above the ball in the air stop orbiting & follow the descending ball down into your empty hand. You should finish holding one ball on top of the other the opposite way round to how you started.
Now do the same the other way. Practise this exercise until you can do it in your sleep. Work on making a nice fluid carry. Use your wrists to make really smooth circles. Also try to blend the change from the orbit into the downward follow, it should be one continuous movement not circle, stop, downward carry.
Carry on practising the two ball move on each side alternately. Work up to combining each side together into a smooth pattern. Focus on the point where you carry the orbit ball down & catch the under the arm throw. Before now I expect you have been making the catch & pausing before performing the move on the other side. Instead of letting the ball drop into your hand bring your arm up to meet it & catch the ball with an upward Claw catch. Continue the upward motion & carry the ball up the side of your imaginary circle. At the same time continue the downward carry with your other hand down the opposite side, this is the start of the circling movement on the other side. Circle the upward hand over & the downward hand under. Make the under the arm throw & the orbit as before. Practise until you can make the change smoothly on both sides.
As you practice notice that after you make the under the arm throw that hand is empty for a beat. In the next step the third ball will be caught & thrown in that gap.
Now take all three balls. Start as you did before with your hands one above the other & hold two balls in the top hand & one in the bottom. Begin the three ball pattern just like the two ball one. Carry the balls around the outside of the imaginary circle & throw one of the balls from the hand holding two up under the arm as you did before. Continue the orbit with the other hand as normal. Wait until it peaks then throw the third ball straight up under the arm, after releasing this ball catch the first under the arm throw with an upward claw catch & go straight into the circle & orbit move just as you have been practising. Make the under the arm throw with the ball you just made the orbit with then catch the second under the arm ball & throw it up on the other side under the opposite arm. Repeat to continue.
After this trick you might want to try Relf's Rubensteins.