While dog owners are familiar with face-licking and tail-wagging, a new study has found that dogs can cry tears of joy to express their emotions. 狗主人对狗舔人脸和摇尾巴的行为再熟悉不过了，但一项新研究发现，狗还能用喜悦的泪水表达自己的情绪。 Katey ...