Inspired by a comment by Fiendish!
She swung her eyes around to where he stood in the doorway.
My first questions when I read a sentence like this: Are they tied to a string? Is she using them like nunchucks? Doesn't that hurt?
Her face fell as he broke the news to her.
Again: Ouch! She should have latches installed or something.
Here's one I just read in a novel by a best-selling author:
His eyes slid over her face.
Ewwww. Just, ewww.
My first mentor at SHU had this thing about passive verbs and floating body parts (FBP), so I learned pretty early on to get rid "was" and "were" as well as FBPs.
So what's a FBP? It's any time in the story where an action is attributed to a body part rather than a character. The quotes above are pretty good (and common) examples.
In the first, she swung her gaze around, not her eyes. Accuracy in description is important. Many readers won't catch it, but the more literal-minded will. And you don't want to ever lose readers if you can help it.
The second example is a little different. Saying someone's face fell is a somewhat common expression, but when writing, there are much more effective ways of getting the idea across. What things happen which create the "falling" of a face? Perhaps the jaw goes slack, or the brows furrow or come together over the nose. If you describe the changes in the face that create the crestfallen look, not only will your reader get the idea, but your writing will be that much stronger for the description. Your character will seem more alive.
The third example is similar to the first, only grosser. Blech.
"But," you say, "my favorite author, Mr X, does that all the time!"
Well-published authors, best-selling authors, and authors who have made a niche for themselves aren't always considered as critically as new authors. If an author already has numbers (sales) on his side, it means he already has a fan base which will buy his books regardless of some minor issues.
Unfortunately, those of us who are just breaking into the business, or attempting to, are held to a higher standard. We have editors to impress in order to get our foot (feet?) in the door. We're competing against hundreds, often thousands, of other hopeful writers, so anything we can improve in our writing can only increase our chances of catching the editor's eye. Tight and accurate descriptions help.
I know when I started writing, my characters' body parts were doing all kinds of things! Once I started recognizing FBPs and began to shift the action from the body part to the character, my characters became more realistic and my scenes, especially action scenes, came across as more focused and immediate.
Have a look at some of your stories. Do you have issues with floating body parts?