A butt-sneeze is a semi-mythical phenomenon that involves a rapid expulsion of air and liquid from the rectum. The 'sneeze' is often mistaken for flatulence due to it's sound and pungent odor.
Despite it's rare occurance, controversy has erupted about whether it is necessary to say "bless you" after a butt-sneeze, as one generally does after a regular Sneeze.
The late Father Y. A. Nire had the following words on this matter:
"In the past, it was believed that the soul escaped the body when a person sneezed. So, by saying 'bless you', the soul was returned to the body. Religion tells us that sinful/harmful substances leave the anus - for example: excrement. However, divine things enter the anus - Such as, my penis into a supermodel. Since the soul is considered divine, it is unlikely to travel out of the anus. Therefore, one does not need to say "bless you".
you: oh shit, I just had a butt sneeze