Oooh I would love CR like this. Someone calling Arthur on his pretending or even just seeing through parts of it sound really great to me!

Arthur would have been pretending once he'd already been under psychiatric watch for a little while, so I don't know if Bucky would be around for that until after he was released, though there will probably be signs of it now. It would be likely that maybe he saw Arthur acting erratically, with a certain disregard for safety and the things he was being taught, as if they didn't really matter to him and he felt very justified in that. It might have even been made apparent that he just didn't think any of it was real. I think those are things that someone with Bucky's attention to detail could have picked up on if they were in rehab together for sure.