What it teaches
The five groups a child meets first, and the features that define them. This is the first classification a child does, and it is the first time they sort the world by a rule instead of by appearance.
The awkward cases are in on purpose. A whale looks like a fish and is a mammal. A bat flies and is a mammal. A penguin does not fly and is a bird. Every one of those is a better lesson than an easy case.
How it works
An animal appears and the groups are the answers. On a wrong answer the feature that settles it is named — fur, feathers, gills, cold blood — before the answer is shown.
What to look for
"Does it have fur or feathers?" answers most of these, and a child who asks that question themselves has understood the point of the game.