As I have been reading fantasy and science fiction books, I have noticed things that wouldn?t be in a real world. This is pretty subtle; you aren?t going to see something that obviously doesn?t belong. An example would be having books be common and cheap way before the invention of the printing press. Sometimes the author gives a good explanation for this (to continue my previous example, there could be a way to mass-produce books using magic in that world) and in that case it doesn?t count as an anachronism. But oftentimes the author does not. I find these anachronisms rather interesting. What are your thoughts?