Oh it gives him away, all right. But where a more sensitive listener might have put two and two together by now, Foster assumes--well, he assumes Tim's upset is related to what he's seeing, his surroundings, but he does not connect it to Tim's earlier behaviour. After all, Tim had it all under control, didn't he?

You lie. You tell them you're all better. They cured you.

"What are you upset about?" Foster asks, and he feels saliva where there isn't any, drooling where he isn't and hasn't in over a month. "What do you see?"