Pug

　　Everyone knows when training dogs, it is important to have a clear signal to tell the dog [No!].

　　In fact, when the dog does right, a signal praising the dog as [Good boy/girl] is just as important. Without such a signal, it forces the dog to [guess] which behavior will be rewarded. This trial-and-error method takes a long time before the dog accidentally guesses correctly, and during the process there is no reward.

　　Think about it: with no reward and a long time needed to succeed, puppies naturally choose to give up learning, or even believe from then on that [learning] is not worth the effort. A simple [Good boy/girl] signal can quickly let the puppy know it did right, making it feel that reward is not out of reach; naturally, the puppy will like learning more. (Source: PetsZone)