While most people can name several elements of vampire lore, there are no firmly established characteristics. Some vampires are said to be able to turn into bats or wolves; others can't. Some are said not to cast a reflection, but others do. Holy water and sunlight are said to repel or kill some vampires, but not others. The one universal characteristic is the draining of a vital bodily fluid, typically blood. One of the reasons that vampires make such successful literary figures is that they have a rich and varied history and folklore. Writers can play with the "rules" while adding, subtracting or changing them to fit whatever story they have in mind.