If the dog's hackles are up, gives a low decibel growl, or engages in a predatory, stalking posture, then there is probably a danger in the environment.

如果狗颈部的毛都竖立起来，或是它发出低分贝咆哮，或是呈掠夺、跟踪姿势，那么周围肯定存在危险。