Recent advancements in sensing, computational intelligence, embedded processing and networking has made robots much more interactive. To make a robot social, the robot must possess five key elements: see, hear, speak, move, emote. Most robots can move, some can even see, hear and speak, but very few can emote. Emotion is an important component of communication. It is expressed through eyes, facial expressions, postures, and hand and arm gestures.
To make a robot social, the robot must have the ability emote. This can be realized through mechanical or graphical features, such as eyes and facial movements, as well human-interpretable body parts capable for posturing and gesturing. Equally important is the ability to perceive and react to others emotion in appropriate ways, either based on socially acceptable moral code, or implicit goals. Perceiving and reacting to emotions involve advanced sensing and machine reasoning, and is where one of the technical challenges lies.
Further Reading
emotionrobots.com 