Back at his apartment, Mark is changing a very adorably wiggly Sofia all about his day. He then answers the phone and assures Callie that the two of them are still all right, and turns around for a moment to pick up the onesie he has laid out. When he turns back, he sees that he probably has to swallow his words as there is no longer a baby on the sofa. He drops the phone and then kneels down on the floor, where Sofia is wriggling and cooing and generally being adorable under the coffee table. He finally picks the phone back up and asks Callie: guess who just rolled over for the first time? Sofia looks positively delighted with herself about it while Mark looks relieved that it appears she's not broken in any way.
Alex is wheeling a chair down the hall while Mark, even more inexplicably, is wheeling a gurney with Sofia's carrier (containing Sofia) on it. Come on, she can't be that heavy yet, she's still a wee little thing. Mark yells his name and Alex freaks out and yells that Hunt said he could have the chair, but Mark actually just wants to get Alex's help; Sofia hasn't cried since rolling off of the sofa the night before and Mark is convinced that this means something is horribly wrong. Mark can't ask anyone in pediatrics to check her out because he knows they will call Arizona but Alex is not inclined whatsoever to help. However, Mark has always been a skilled intimidator and when he threatens to "end" Alex, Alex picks up Sofia's seat, sets her in the rolling chair, and wheels her along down the hall. She's probably not crying because these are some fun rides she gets to go on.
The reason Owen gave up his office chair is that he seems to be actually giving up his entire office. A bunch of guys are in there carting away his stuff and he's sending furniture to different departments that need it. I would think that even if he was trying to break the mold of having a traditional office he'd want to keep some of this stuff as, like, a home base. But maybe that's just my organized female mind talking. Bailey comes to the door and at her raised eyebrow he starts stammering like a fool, desperately justifying what he is doing. Without Bailey saying a word he carries on an entire argument just by guessing what she is going to say: He's just getting rid of things he doesn't need, he knows people will think he's crazy, but he has decided that his office will be where he is. Bailey just stares at him and then, as if daring him to stop her, sees a lamp she likes, picks it up, and walks out.