A woman was watching a few people dancing around.
Then, as suddenly, as silently, as corn falling to the scythe, they all fell flat to the ground.
Does it mean they fell to the ground just like corn falls when its cut by a scythe?
That's the only way I would know how to interpret it. It's not a common idiom. Or if it is, it's one I've never seen before.
There should not be a comma after "silently."
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.