Zookeeper
Contains a little-known free game feature. The free game
icon pops up on one of the platforms on the
3rd screen (coconuts). It comes out like one of the bonuses,
but instead it says "Free Game" in a little box.
When it appears, it has it's own little tune too (and it
usually pops up opposite of where you are, so if you are
at the bottom of the screen, it will come out at the top).
If you have a Zookeeper, go into options and set the "Free
Game Rate" to 99 to make it appear more frequently.
If it's set to 0, it won't come out at all. The Zookeeper
Flyer actually has a note saying that the free game feature
maybe prohibited in some states!