Freezing in place, Oswald briefly looks like he's been caught doing something he knows he shouldn't have, like sneaking cookies before dinner.

Really though, why wouldn't Ed pick up on something like that, to assume that Oswald already has the knife on his person? It's relatively predictable Oswald behaviour, actually.

He ends up chuckling somewhat nervously, reaching across to take the refilled glass.

"When you put it that way, it gives it a sort of sentimentality, doesn't it?"

One of the few things he got from home... Maybe Oswald should be offering it back, but the weight of it in his pocket makes him feel more secure.