The Snake is a pattern in which
each hand takes a turn throwing all the balls in a row, as if juggling a
Five Ball Cascade. While it's fairly simple, the Snake can be tricky to
juggle due to its odd timing; you want to be just about throwing the last
ball from one hand while the first ball is being caught in the other.
The best way to learn the Snake is to start with all three balls in your dominant hand. Throw all three balls from your dominant hand to your non-dominant hand such that the last one is being thrown as the first one is being caught.
Practice this on both sides. Pay particular attention on the timing of your throws. Once you are comfortable with one cycle of the Snake, you can simply add more on by throwing each ball back across your body as they are caught.