Studies have shown that most adverts would rather use smiling faces or happy faces than any other because humans are wired to respond to and happiness.
This is attributable to our neural programming. In humans, a set of neurons called the <em>mirror neurons</em> cause us to experience the emotions being communicated by a facial expression that we look at.
So people are more likely to accept a product or service or a message that makes them happy. To achieve this, the advertisers put a happy face or a smilling face to the advertisement.
