"You really haven't lost your touch at all, have you, Professor?"
Percy looks at Miles. He wouldn't expect anything less than the man who singlehandedly pioneered dreamsharing, sucking everyone else around him in into the fascinating world of the dream. He wonders, vaguely, if Miles would think of him any different, if he'd known, the baby that Mal's carrying right now, it's actually not Dom's. It's Percy's. Mal told him so - which is why Percy allows Arthur to get him drunk after Havana.
"I'm going to keep the baby," she'd said. "I'll love it more than anything in the world."
He could have asked her to leave. Mal is having his child, not Dom's. But it was Percy's mistake to begin with, in the first place. He made Mal remember how they were, miss how they were. So he doesn't say anything and watches Arthur go up the stairs.
"...Sure, I'll buy you a drink. Come on. I heard about Mal's baby. Congratulations."
Arthur keeps enough of a distance between them as he goes up the stairs, but he's made it just in time around the corner, to see Eames disappear behind one of the doors. Great, he can go downstairs now, say he's already said hi, Eames is in the middle of a shower, or something similar.
At the same time, Arthur suddenly has a horrific vision of Miles and Percy guarding the stairs. Yes, he thinks he'd rather stay up here.
So Arthur lets himself in, because these doors are horribly secured and he's going to install a new lock and remove it when he leaves. That's a good idea. Eames' room has a balcony. Arthur and Percy's room are on the ground floor, so they don't have one.
"...You did stellar work on my passport, Mr. Eames." Which is probably not the heartfelt 'hello' that Percy and Miles hope for, but it's a start.