Too often I read stories--especially various forms of crime fiction--in which a person or a body is described as "prone," and yet the context makes it clear that the person or body is actually "supine."
It frustrates the bejesus out of me.
Direct from the dictionary definitions:
Prone = "lying face downward"
Supine = "lying on the back, face or front upward"
I hope you're not prone ("having a natural inclination or tendency to something") to making this error.