Based on a 19th century lottery to boost attendance at the Rio zoo, the animal game is no ordinary numbers racket. It starts off with 25 animals, each of which is assigned four consecutive numbers (from 01-04 for the ostrich to 97-00 for the cow).

Each of the 25 animals is assigned a sequence of four consecutive numbers between 1 and 100. The most common way to play is to bet one real on an animal, but one can also choose a combination of numbers and numerals designated by an animal.