[That blank look is just the nail in the coffin. Steve thought he was operating on reflex, grabbing the plate for Bucky, but suddenly he wonders... did he mean to do this? Was it meant to be some kind of test?

It doesn't matter - it ends up being a test, and Bucky fails. Badly.

He lets it lie for a minute, but he knows he can't walk out of here pretending any longer - not pretending to himself, and not pretending with this Bucky. He glances up, then back at his food, because he's not sure he can say this to a face that looks like Bucky's - is Bucky's.] I should probably congratulate you on getting me to believe you for this long.

But you're not him. And we both know it.