anecdotal corroboration: my cat recognizes and responds to 5-6 different words/phrases for food, even from a visitor, but does not understand a single other word in any language spoken in the house: food, snack, treat, cookie, nom-nom. he responds to each of these uniquely (we use them to refer to different things he can eat).
Alternate hypothesis: your cat has a fluent understanding of the English language, and has a vocabulary as large as yours - but he doesn't deign to care about words that don't relate to your purpose (i.e., providing food).
