Joey knows what a cow says ("broo"/"moo"). The past few days, we've been working on what a dog says ("oof!"/"woof!").
Tonight, as Joey was nursing to sleep, he stopped several times to WOOF and a few times to point and say "dah!" (dog). He was wearing pajamas that had a picture of two dogs on them, and though they were hidden under his sleep sack, he must have remembered that.
It was really cute. =)