There are often ideas that seem totally obscure, then three stories come along more or less simultaneously on similar lines. Or independently occur to different authors who are unaware of eachother's work, of course. For example, I was once criticised for plagiarising a Harry Potter story I'd never read, because I'd killed the same character in the same rather silly way as in the original story, and described it in similar terms.
But when it comes down to it, there really aren't that many different ways to describe Rita Skeeter flying into a bug zapper...
