The fact that Tim would call this anything but the most pointless conversation he's ever had makes Foster's stomach turn with revulsion and anger--anger at what he knows is wrong, but anger which he is not entitled to, and which makes him feel even more ill as he smiles back.

"Okay!" he says brightly--without a hint of audible resentment.

And then, in an almost identical tone--bright and pleasant and absolutely at odds with his previous one: "Goodbye!"