Aside from word count, the most distinctive trait of a flash story is the twist. You know, that sudden change in meaning or surprising detail that makes you smile or gasp or read out loud to the nearest bystander.
The twist is arguably the toughest part of the story to craft. One way to create a twist is to withhold a key detail until just the right moment, like Max Garland does in his flash story Sin. Another way is to examine your recollections for the sudden realization or change in circumstance that altered your perception, creating an ah-ha moment. Then you just need to craft the story to lead your reader smack into that surprise, similarly to how it happened for you.
For example, one of my favorite places in all the world is Lake Powell, which is 100 miles of the Colorado River trapped in the Grand Canyon. It’s a breathtakingly beautiful place of long, winding canyons with high walls and then higher walls still. It’s hot and dry and orange, and full of dazzling blue-green water. It’s remote and quiet, with no man-made light.
Did I mention it’s dry? High altitude, desert-dry. But you can be tootling along in your little boat, zigging and zagging, when you come around a tight corner into a gigantic bowl full of thundering, 12-story-tall waterfall leaping head-first out into the middle. After oohing and ahhhing, and swimming, and taking pictures, you finally move on to see what’s around the next corner. When you come back two hours later, having reached the end of the canyon and picnicked for lunch, there’s no trace of a waterfall. None. No deafening sound. No spray. Just a huge, silent, beautiful bowl. Gone until the next cloudburst a county away.
So, if you can take your reader to that same moment that took you off guard, or reveal a surprising detail at just the right moment, you’ve created the twist.