I do think it always helps to put on the reader hat and imagine what the reader will take from this. And I think the occasional reference to independent body part movement is unlikely to bother readers brought up on more florid prose than we generally go for now. (One of my favorite authors, Dorothy Dunnett, wrote in the 60s and was fond of constructions like: "His sapphire eyes collided with her sable ones." And it didn't bother me much at all... because her prose was lush and descriptive, and her stories were so dramatic.)
And there's no doubt that sometimes the rhythm of the paragraph calls for a longer line-- you just know that this last sentence in the paragraph needs two more syllables to sound right. If so, no problem for me with "He reached out a hand" rather than the more sensible "He reached out."
But understand, the power of that rests on its unusualness. That is, if everytime you mention characters doing something with their bodies, you mention a body part:
His feet tapped on the street
she kicked out a foot
her ears perked up
his head swivelled
He ran a hand through his hair
Her mouth gaped open
...then you're going to lose the power of the occasional rhythmic use. Voice is all about selection-- choosing judiciously to use "he reached out a hand" rather than "he reached out"-- choosing that because it is right, because it conveys what you mean, because it carries the cadence of the action in the sentences. To me, "he reached out a hand" is going to slow things down (two extra words) and so is more suited to tentative, tender, gentle action, like "he reached out a hand and touched the tears on her cheeks."
Now your voice might dictate how this is done. For example, unlike many editors, I love modifiers. The grandeur of the English language comes from our multitude of verbs-- and our very versatile modifiers. Just as you can embed a metaphor into a verb ("the highway sliced through the prairie"), so you can use a modifier to turn one of those body parts into a carrier of emotion.
He reached out a tentative hand.
She slid out a negligent foot.
Or like stout Cortez, when with eagle eyes, he star'd at the Pacific.
(Sorry-- stole the last from Keats. :)
That is, think about the body part as a metaphor for action and conflict, as well as an actual body part. How can you use that to enliven this passage? How can meaningful verbs and modifiers add to the power of that line?
Again, if you always, heedless of connotation, use body parts willynilly, then you'll lose the power that comes from doing it judiciously. As with all voice matters-- do what is right, not what is easy.
Theresa, at some point, we should talk about voice, and how it's no more "natural" than Maria Callas's singing voice. :)