Trees and airplanes.

Nate loves trees. Anytime we go outside he stops and talks to all the trees on our walk. Once he pulled off a big piece of bark and had this look like "Oh my goodness, I broke it!"...goofy.
Since we live right beside a small airport, there are always lots of smaller, low flying planes and Nate loves those too. Anytime he hears one, he stops and won't move until he's found it in the sky and shouts "airplane," which sounds more like "arrrhpin." Close enough.