You're at a friend's house and along comes her collie, Baby, wagging her tail. Good girl! You bend over to pat her and are rewarded with a growl¹. What went wrong?

你去到朋友家，她的牧羊犬小宝摇着尾巴迎了上来。真乖！你弯下身子拍拍她的头，她却对你低吼了一声。哪里不对劲了？

"It is so important for people to realize that a wagging tail does not equal a dog that is friendly or wants to be petted," says E'Lise Christensen Bell, veterinarian and board certified² veterinary behaviorist at Veterinary Behavior Consultations³ of NYC. "It can, but you are much better off looking at the entire dog. If there are stiffened⁴ muscles, dilated⁵ pupils, tense facial muscles, or ears pinned forward or back, these are signs that you should back off."

“人们应该要知道，狗摇尾巴不等于示好，也不一定是想要和你亲昵，”兽医兼纽约动物行为协商会的认证动物行为学家艾丽丝·克莉丝汀森·贝尔说道。“摇尾巴可以表示友好，但是最好还是整体地看。如果它肌肉僵硬、瞳孔放大、面部紧绷、耳朵或前或后紧贴着头，你就最好离它远一点。”

For help with figuring out what the tail wag means, look for the direction of the wag or at how fast his tail is moving. Studies show that dogs wag their tails to the right when they are happy and to the left when they are frightened.

观察尾巴摇的方向或者速度也可以帮助你解读摇尾巴的含义。研究显示狗在高兴的时候尾巴会往右摆，害怕的时候会往左摆。

If Baby wags her tail high and back and forth⁶, she's in her "happy place". When she's just being plain nosy⁷, she will keep her tail horizontal to the ground. When Baby's tail is tucked between her hind⁸ legs, she's either frightened or being submissive. When she's wagging it low, she's worried or feeling insecure about something.

如果小宝尾巴摇得高高地还前后晃，她就是高兴的。如果她只是好奇，她的尾巴会跟地面保持水平。如果小宝的尾巴垂到了后脚，她要不就是被吓到了，要不就是表示顺从。如果她的尾巴摇得很低，她就是在担心什么，或者是没有安全感。

Dogs wag their tails for other dogs, humans, and other animals like cats. But research shows that dogs don't wag their tails when they are alone because there is no need. Just as humans use smiles and body language as social cues in different situations, our canine⁹ friends do the same.

狗会对其它狗、人和其它动物（比如猫）摇尾巴。研究发现狗独处的时候不会摇尾巴，因为没有必要。人类在各种的社交场合会用微笑和肢体语言表达情感，我们来自汪星的朋友也会这么做。

"Dogs are much better at reading each other's body language than we are," says Dr. Bell. "Dogs that are behaving appropriately in social systems use their bodies and tails to communicate with other dogs even as they are observing the tails and body position of other dogs. This helps them avoid unnecessary conflicts."

“狗对肢体语言的解读能力比我们强多了，”贝尔博士说。懂得正确社交礼仪的狗在观察其它狗的尾巴和身体姿势的同时就已经开始用身体和尾巴交流了。这能帮它们避免不必要的冲突。”

Dogs also wag their tails to spread their natural scent¹⁰ from their anal glands¹¹. Each dog has a scent that's unique to him or her. An "alpha" or dominant¹² dog that carries his tail high will release more of his scent than a dog that carries his tail lower. Often, when we see a dog holding his tail between his legs, he's frightened and doesn't want to release his scent. This is his way of flying under the radar¹³.

狗还会通过摇尾巴来散发肛门腺的气味。每一只狗都有独一无二的气味。强势的狗会把尾巴伸得很高，这样就会比尾巴放得低的狗释放更多的气味。通常我们看到尾巴垂到两腿之间的狗都是被吓到了，所以不想散发出自己的气味。这是他们隐藏自己的方法。

Since dogs haven't yet figured out a way to talk to their owners and their other animal cohorts, they have to use their bodies to communicate. The eyes, ears and body positions are a few clear indicators¹⁴ of how they feel. But wagging their tails is one of the most visible and well-known ways canines¹⁵ use to clue people and other animals in on exactly what's going on with them.

狗现在还没有找到跟主人和其它动物说话的方法，所以它们得用身体交流。犬科动物的眼睛、耳朵和身体姿势都能清楚地反映它们的心情，但对人类和其它动物来说，摇尾巴是最容易看见、最被熟知的方式。