The kid has started categorizing the world and associating properties with those categories. He has also started learning the names of things. Examples:

• He will see a dog, and say “Dah!”
• He will hear a dog bark, and say “Dah!”
• He will hear an airplane, and say “Buuuuuu,” and point up at the sky even if the plane isn’t in our field of sight.
• He will spot a bus from blocks away, get very excited, and say “Buh! Buh! Buh! Buh! Buh!”
• He will see a cat and meow at it as best he can.

But the categories are still pretty general, and the edges are blurry:

• He will see or hear a truck and say “Buh!”
• He will see a cat, and say “Dah!”
• He will see a squirrel, and say “Dah!”
• He will see or hear a dog and meow at it.
• He will see a human child, say “Dah!,” and then meow at them.

So it seems that right now, in his mind, “Dah!” is any animal, or at least any mammal, bigger than a pigeon and smaller than an adult human, and he further believes that all non-verbal “Dah!” meow. Even more oddly, sometimes he will react verbally to no apparent stimulus – he will say “Dah!,” or “Buh!,” or start meowing, without anything around that I can detect. Sometimes he seems to be remembering previous sightings – he has definitely reacted to neighboring apartments that house cats or dogs, even if nothing is currently visible in the window – but that’s not always the answer. Is it that he heard a sound which he associates with “Dah!” or “Buh!” but which I don’t? Is he simply remembering “Dah!” or “Buh!” and talking about them? Is he trying to call one? It’s a mystery, but at least it’s one of the cuter mysteries.

Except when he looks behind me in an otherwise empty apartment and waves good-bye to nothing. That’s kind of creepy.