Good manners dictate that every sneeze should be followed by some variation of "bless you." Whether it's a wall-shaking nasal explosion or a dainty achoo, no sneeze is complete without it. But have you ever wondered why we do it? (Other than the fact that mama raised us right, that is.)

Unfortunately, the true origins of this bizarre social convention are a bit murky. But there are plenty of fascinating guesses, and not surprisingly, most of them are based heavily on superstition.

The most popular theory is that it originated in Rome when the bubonic plague was ravaging Europe. Sneezing was one the plague's main symptoms, and it is believed that Pope Gregory I suggested that a tiny prayer in the form of saying, "God bless you" after a sneeze would protect the person from death.

Another, more superstitious theory, is that it stems from the ancient belief that a sneeze might accidentally expel the spirit from the body unless God blessed you and prevented it. Other cultures thought that sneezing forced evil spirits out of the body, leaving others exposed to the wandering spirits. A blessing was to protect both the sneezer and those around him.

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And then there's the rumor that our hearts stop when we sneeze, and that saying, "bless you," is a way of welcoming the sneezer back from the dead.