10 points!!!What you look for in book cover?

When you go to a book story and you see that one book cover (without knowing anything about the story) that pops out at you, what is it? Like the genera of the cover or color? Or anything you can tell me. For me it wuld b something mysterious like a dark forest or blood dripping with a black back ground. Things creepy and mysterious like that. My friends is a happy looking cover like a girl laughing or blowing a dandelion...stuff like that. What wuld urs be and plzz give as much detail as possible! Thx! :)