The journal "Behavioral Processes" has published an article about a dog named Chaser who was taught to recoginze1,022 nouns. PBS' Nova episode will broadcast an episode on her in early February.
My dogs are way underachievers in this regard. Chaser is the Fulbright Scholar of dogs. Mine are more like school dropouts--they like to learn, but are inherently lazy (especially now in their old age), and like to do things humans find unpleasant, like eat poop. They're so dang cute, though, and they clearly understand way more than I'd care to admit.
Words/commands they do know: Up, down, sit, stay, come around, take a bow, spin, ride, outside, inside, shake, cookie (of course!), cat, Where's ----(fill in cat name)? stand, rub-down, give me your foot, lift, walk, wave, enough, look at me, nice ignore! chase, work, doctor--the usual doggy knowledge required to live with a human. But I like to read aloud to them, and we just finished "The Fall of the House of Usher" for my book group. Perhaps they know more than I think? Perhaps they know more than me.Their deep brown eyes seem to betray an age-old wisdom far beyond that of a creature solely concerned with finding something stinky to roll around in.