It probably wouldn't be a good idea to tell her that he noticed she was a bit like her mum when her mouth went all tight and angry like that. Like when Molly was having it out at Fred and George about something.
He ducked out the door, turning around to look. As soon as he stepped out of contact with it, the wall melted together, looking seamless. So right. One way only. Even if she left the door open. Which Harry thought she probably hadn't. Brilliant for the D.A.
And not actually that bad for him either, since it meant he got to hide in the cloak and walk the long way around back to the Room's entrance. By the time he got back, Ginny might have. . . stopped looking like she wanted to cry. Or kill him.