Math Math Meow

Catboy Zero is obviously not intelligent compared to a human, but compared to other catboys he's insanely smart. He has the ability to understand language and construct short sentences with correct syntax, even though his vocabularly is slightly limited, but that's a really big deal. He understands basic addition and subtraction and is fascinated with the concept of zero, heh. And his version of 'playing' is to have his owner do simple algebra with him. 

Zero likes to count things and tell Gai how many pieces of candy there are in the jar (he's counted every single blade of grass in the yard). He tells Gai that he has 5 scrapes on his face and Gai gets flustered.