Why do dogs seem to understand and respond to our moods?

Not for nothing dogs are known as man's best friend. These animals can sense everything. They know when we're sad, happy, annoyed, worried, excited and or so many other moods human express through actions, gestures, and body language. Incredibly, dogs can read all types of signs we produce, but not only that they can also understand how we feel. It's like if they had a sixth sense. Besides, their amazing olfactory skills allow them to smell things we can't even think of as humans. These include moods, which can be evidenced also by voice.

I suppose that because of all these outstanding features these creatures have is that they're the best companions a man could ever want. These animals are known for helping old people, blind people, sick people and people with disabilities have a better life, and maybe even cure them.