Susy and Sam seem to practice personal hygiene, and the rest of the apartment seems clean enough, but the kitchen is a mess. There is dirt smeared on the refrigerator, the sink is dirty, there is spilled crud running down the front of the washing machine, and the walls are dirty. It's unusual for characters played by glamorous movie stars to be presented as slobs who don't keep their kitchen clean.
shareI always noticed that their kitchen and even the wall around the stairs look grimy. It definitely makes the movie feel lived-in and strips away any sense of vicarious glamour. I actually kind of dig that-- it's so weird to see in a big Hollywood movie like this, especially with Audrey Hepburn of all people. They also have onions hanging by the cabinet-- that's gotta smell lovely.
And of course, by the end, the place also smells like gasoline and if you look closely, Roat bleeds all over the white cabinet when he goes after Susy with the knife. I don't think they can put off cleaning the kitchen any longer after that.