Cat Stax is a puzzling thing.
You get 12 cat-like pieces, each of a different color and shape. You get two decks of 24, two-sided cards. One deck is for the puzzles, the other for the solutions. This makes it very easy to control your cheating impulses, or to lose control entirely – which, as you progress through the puzzles, you may in fact do.
Each puzzle shows you a grid and which of the cats you’ll need to fill in the grid, perfectly (no hanging cat parts allowed). This is all fun and familiar to your average cat puzzle-solver, until you arrive at puzzle #7 – the first 
TWO LAYER cat puzzle, wherein the reason for the name of the game becomes tantalizingly evident. Two layers, as in some cats don’t lie down like the good little puzzle-piece-cats you think they should be. They stand up. And later, you discover that some cats don’t just stand on their feet, but on their back ends or front ends or heads, even. And, later on, by the time you get to puzzle #23, you get three layers of cats! And on and on until you find yourself trying to figure out how to make a three-layer cat stack using all 12 cats!
The puzzle comes in a travel box with a transparent lid (easier to keep track of your cats that way). The manufacturers are quick to note that it you might very well arrive at a totally different, but entirely acceptable solution all on your own, because, as we have all been so oft told, there is more than one way to stack your cats.
As you make use of the two decks (puzzle deck and solution deck) you’ll come to appreciate ingenuity and compassion embodied in this minor, but brilliant innovation.
Cat Stax was invented by Bob Farron and designed by Mike Mendolese. from Brainwright