What causes the phenomenon that when you see somebody else yawn (even if they're only on TV), you do too?

Answers:
The yawn reflex is often described as contagious: if one person yawns, this will cause another person to "sympathetically" yawn.[2] The reasons for this are unclear; however, recent research suggests that yawning might be a herd instinct.[3] Other theories suggest that the yawn serves to synchronize mood behavior among gregarious animals, similar to the howling of the wolf pack during a full moon. It signals tiredness to other members of the group in order to synchronize sleeping patterns and periods of activity. It can serve as a warning in displaying large, canine teeth. This phenomenon has been observed among various primates. The threat gesture is a way of maintaining order in the primates' social structure. The contagion of yawning is interspecific (i.e., try yawning in front of your dog). Yawning in public is generally regarded as impolite in the West, but came into fashion in polite French society for a brief period in the late 18th century. Oddly, sometimes sympathetic yawning may be caused by simply looking at a picture of a person or animal yawning, or even seeing the word "yawn".

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it's an evolution thing - monkeys do it too. they reckon that it first evolved so that all the members of a group of monkeys/chimps/other animals would go to sleep when a few got tired. it's just stayed with us so if we see a yawn we do it too=edit=interesting thing: while reading other peoples responses, i started yawning myself (even though i'm not tired). so it looks like it even works for reading the word (as "kevin's gal" suggested)

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Domino effect.

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I do not copy yawning by other people, but apparently I am in a minority; it is normal to do so. See:http://faculty.washington.edu/chudler/ya.for a good discussion of the phenomenon and possible causes, with links.

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Actually yawning is a sign of lack of oxygen to the brain.TRUST ME I AM A NURSE.When people are dying the yawn alot b/c of poor circulation of oxygen to the rain.

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Yeah.I yawned right now!

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The yawning you are talking about is termed as Sympethetic yawningIt is unclear yet.

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i read this and yawned.rich, will be the person, that solves this mystery..

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