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Thread: Why does human yawn?
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[quote=FRANKENSTEIN,285772]Do you usually yawn? Scientists say a person begins to yawn when he/she is a 15-week-old embryo. We all think that yawning is sign of fatigue, but scientists say that yawning might be an ominous sign which indicates there are some harmful gases in our lungs. They also claimed that yawning might be socially contagious.[/quote]
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