1. How is it decided which animals are used in the game?
The animals in Metazooa were selected based on how familiar they are to people, as well as for the breadth of species that would make the game more interesting.
2. The game is wrong! Wikipedia has different classifications for one of the animals.
This is possible. The classifications used in the game are based on the NCBI taxonomy, which is the most widely used taxonomy for animals. However, it is not the only taxonomy. The Wikipedia taxonomy is also widely used, and it is possible that the two taxonomies disagree on the classification of a species.
3. Why is there no "Reptile" or "Reptilia" class in the game?
While some datasets, like Wikipedia, use the class Reptilia, the NCBI taxonomy does not. Instead, the NCBI taxonomy uses the class Sauropsida, which includes all reptiles and birds. This is because some of the animals commonly identified as reptiles have more in common with birds than they do with other reptiles. For example, crocodiles are more closely related to birds than they are to lizards.
4. Why is "domestic cat" a possible guess but not "domestic dog"?
This is because domestic cat's have their own species ("Felis catus"), but domestic dogs are usually classified as a subspecies of the wolf ("Canis lupus familiaris").