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There is an effect that not only have we all witnessed， but have26. Haven"t we all been on an elevator and noticed that just about everyone stops talking when they get on？ Why do we do that？ You can be having a 27 pleasant conversation with someone， and as soon as you get on an elevator， you just feel like you"d better shut up.
Then， as soon as the doors open， everyone28conversation. Primatologists， or people who study primate （灵长类动物） behavior， have a term for this. It"s called the "elevator effect，" though it doesn"t 29 only on elevators. It happens whenever a group of primates， like humans， is 30 a situation where escape is 31 impossible. It"s thought to be a kind of safety32: as long as nobody talks， nobody is going to risk getting in a fight when there"s no way to spread out. The elevator effect keeps a lid on potential problems before they start.
Even though they rarely if ever ride elevators， chimpanzees demonstrate the elevator effect as well. When chimps are temporarily crowded together into small areas， they will 33 their vocal communication， that is， nobody speaks， and avoid eye 34. The amount of scratching the chimps do， however， goes up. Since scratching is a sign of stress in chimps， we can imagine what they are feeling. It"s just like what we feel in a crowded elevator——everybody carefully35 the lighted numbers and no one saying a thing.
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