Rat

From YPPedia

A rat is a type of pet. Unlike other pets, they are not purchasable or tradeable. When a pirate takes the 'Furnish your home' mission, he or she receives a randomly-colored rat.

There are twelve different colors for rats. Green rats were only available for a limited time during Spring and Summer in 2008, in order to celebrate the release of the Malachite Ocean. Persimmon rats became available with release 2009-07-01 celebrating the release of the Crimson Ocean.