Someone recently told me that reading romance novels made her sad that her eyes didn’t ever flash.
I’ve met someone with flashing eyes, as it happens; she had some kind of crazy eye surgery thing and now her pupils gleam and go mirrored if you look at her from the right angle. It’s creepy.
But for the most part eyes don’t actually “flash.” It’s a widely-understood gloss for “that expression where you narrow your eyes as the corners of your mouth turn up and your eyebrows raise, creating an illusion of movement that draws our hunter-evolved eyes to yours.” Which is unwieldy in a steamy seduction scene, no question.
This is reasonably common practice. It’s essentially a prose-tightening shorthand that readers have all implicitly agreed to translate for us. Hence “rippling sinews” (which you will only actually see ripple if someone is suffering from grievously deep wounds already), throbbing members (ladies — it’s not actually a GOOD thing if I can feel that “throbbing”), and so on.
But my favorite is still “flashing eyes.” ‘Cause lasers. What’s yours?