He says the former any time he sees something he thinks is cool, including trucks, animals, bright lights and loud noises. The latter he says constantly, any time something suprises him in the slightest - the smallest trips, slips, or bumps. It is also important to note that his "ow" is a tiny utterance, not loud or exclaimed, just simply "ow" in a a non-extraordinary tone.
It's also getting quite fun to have conversations with him. He answers "Yeah" to every question you ask. Here is an example from this evening:
"Did you have fun at the park with Daddy?"
Did you go on the swings?"
"Did you see some trees?"
I could go on.