Mystery solved!

Aaron's high chair faces out the back window. You can see two neighbors' yards from there, the cul de sac their houses are on, and a little strip of the road that goes past the cul de sac.

Often, when we are feeding him, he points emphatically out the window, often accompanied by a "Zhuh" sound. We look out the window, expecting to see someone out in the yard or a bird, or maybe a car on the cul de sac (he loves to see the garbage trucks up there on Monday mornings). But usually, we see nothing. A little while later, he does it again. I just figured he was unusually excited about the trees or the wind chime, or something else that is just always outside.

But on Friday, we figured it out. I was feeding Aaron and Thom was sitting with us, facing out the window. A car drove by on the road above the neighbors houses. Aaron pointed. I turned to look, the car was gone. But Thom had seen it. So all those times he emphatically pointed out the window, he was most likely seeing cars drive by, but they were long gone by the time we turned around. Suddenly he doesn't seem so crazy!