I read somewhere that a cat can understand as many words as a toddler. Cats are very smart and trainable. Just how smart is that we seen that cats have trained their owners to get out of bed early and feed them.
My cat, Cocoa Kitty understands quite a few words. The usual, tuna, turkey, chicken, toy, and treat but also commands like sit, spin (he turns in a circle), "git-git" (get out of there), up, stand, and walk. I don't know if he understands good boy and all the various way I praise him but he sure enjoys it. He loves to be sung to, and will purr very loudly.