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Mouth breathing, medically known as chronic oral ventilation, is long-term breathing through the mouth. It often is caused by an obstruction to breathing through the nose, the innate breathing organ in the human body. However, by the early 20th century, the term "mouth-breather" had developed a pejorative slang meaning connoting a stupid person.

Etymology

In the early 20th century, "mouth-breather"

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