what's that sound?

When swimming with Dennis at the lake today--and I did it with no other adults in the water besides myself, so we're really making progress--he said "I hear horn go beep beep" and I told him I didn't hear it. Then he said "I hear train go choo choo, listen Mommy", and I strained my considerably older ears and heard a dove cooing across the lake. I imitated the sound and he said "that's it, Mommy, you hear it", and I taught him that it was a dove. From then, whenever he heard it, he said "hear the dove, Mommy? I hear the dove." We talked about all kinds of things while we were swimming, conversations initiated by Dennis mostly, and I can't say when I've enjoyed a swim more. He talked about the fish in the water and talked about bubbles and how the boat looked dirty and he yelled to Gran "come down here, Gran, and watch Dennis swim." When she got down to the dock, he yelled "jump in, Gran, swim with Dennis". She didn't, due to a nasty cut on her finger, but she watched and enjoyed for a while.