When Tim's daughter asks him if he has ever killed a man, and he says that he hasn't. Even though he says this, he thinks of the small man that he did kill in Vietnam.
Tim recalls the moment in which he threw the grenade, out of pure instinct, and then watched the man attempt to run, before dying to Tim's grenade.
Tim explains that in moments where he is alone, he still sees the man through fog. He is able to see exactly what the young man once looked like, with his head cocked slightly to the side, as if listening for something.