Dogs bark in different sounds and for different reasons , some dogs bark continuously some bark when sees a stranger . Pets in house bark in night if they hear some noise ,or street dogs bark so they also start barking . Dogs have sense of smelling they remember person's smell ,if they are left alone in the house or tied up they start barking. some people say if the dog sees ghost, or some paranormal activity they bark continuously and some dogs bark at walls , back yards, but it is just normal .so the question is unanswered there are incidents of spirits but it has no conclusion. Dogs if left alone in the house with no owners they bark their are incidents of real spirits but it can be natural also.
They stare continuously in eyes if they are patted and loved they cool down. so dogs bark for different reasons in night if they hear noise if they want to go for stroll you can take them out and if trained tell them keep quiet everything is fine .If your dog in house is loved more it becomes insecure or jealous and starts barking so to bring attention of owner towards him or her. IF your dog taken out sees street dogs it will start barking try to run , groin, or when it becomes excited.
In the night if your dog is in dark room it will bark and so dogs have several reasons to bark to communicate with us. If dogs are hurt they cry , or say howl, if they are hungry they bark,so their are many reasons they bark .