The mouth or 'oral cavity' is the opening of the alimentary canal, where animals take in food and begin the digestive process generally with both motor and chemical aspects of digestion. In mammals, it is also connected to the respiratory system. The human mouth includes the lips, teeth, tongue, salivary glands, and mucus membranes.
Because the mouth (specifically the lips and tongue) is connected to the respiratory system, humans have developed the ability to talk, as air is passed over vocal chords in the throat, creating a humming noise that is shaped by the mouth to form words. This ability is unique in humans, though other mammals do possess more simplistic systems of making noises and "calls", they do not have the control over the vocal track to create words.