Plagues and other great diseases are important parts of history and some settings. They defy man and may even defy God in their swift and terrible punishment upon the body of society.
In a small, genetically isolated region it is not uncommon for the locals to have three arms. The third arm is generally a second right arm that is a good bit weaker than a normal arm and is generally held against the chest. This hird arm is most often used to carry small things, though some of the more skilled craftsmen have learned little tricks with their third arm.