This trick sort of uses Fork catches. I say 'sort of' because the ball spends a brief amount of time on the back of the hand, but the contact is so short that you can get away with just placing your hand underneath the ball. You will find this trick much more controllable if you can hold a ball in a solid fork though. It can be a one off move or two different continuous patterns.
Take two balls, one in each hand. Hold one normally at waist height & one in a Fork at just below shoulder height. Throw the ball at waist height directly up into the palm of the other hand. Just before it hits your palm flick the ball off the top of your hand using your fingers so that it rises to eye level & lands in the opposite hand just like a normal cascade throw. This gives the illusion that the ball in the fork was propelled off by the force of the second ball thudding into your palm.
Be as accurate as you can with the upward throw. It hasn't got to travel very far but if it doesn't fly directly into the palm you either have to flick the top ball too early & spoil the illusion or move the top hand to make the catch, a ball can be easily dislodged from a fork grip by sudden movements.
Practise on both sides.
Take three balls & juggle a cascade. As one ball peaks, instead of making a normal catch, quickly insert the back of your hand under it. Hold the ball in position at its peak in a fork. At this point the opposite hand is holding one ball & the third ball is just peaking above it. The opposite hand throws the ball it is holding straight up into the palm just like you did in the two ball exercise before catching the other ball. Flick the fork ball off just before catching the one thrown up into the palm & then continue juggling.
That is the one off move, get that solid & then try the two possible ongoing patterns, one is asymmetrical (one sided) & the other is symmetrical. I will describe both patterns then write a paragraph with tips that apply to both.
The Asymmetrical Pattern
The asymmetrical pattern is a little bit like a Half Shower. Just repeat the flick off continuously on one side. Start as described above for a single flick off. After you have flicked the fork ball you throw a standard cascade throw underneath it, catch this ball in a fork at its peak & continue the cycle.
The Symetrical Pattern
The symmetrical pattern is very similar to Juggler's Tennis in that one ball is thrown back & forth over the other two. As you flick the ball off the top of your hand catch it in a fork with the opposite hand, the immediate next throw is made up into the palm & the fork ball is flicked straight back again. In this variation each ball stays in the same position so using different colour balls will help you to keep track of what goes where. Just remember one ball is flicked back & forth & caught fork style, one ball is thrown almost vertically up into the opposite palm & the other ball is thrown back & forth as a standard cascade throw.
These two versions are very fast, flick the fork ball higher if you need more time. It is tempting to just hit the fork ball with the back of your hand, but make sure you make a definite cushioned catch & throw, batting the ball will quickly result in a drop. Focus your attention on the flicked ball & watch the other two in your peripheral vision. Bring your elbows up & out to the side as you make each fork catch, this will make room underneath the forked ball for you to throw & see the other two balls. Try & keep your elbow slightly higher than your hand when flicking the fork ball, this will help you throw across the body to the other side rather than straight up.