题目

Studies have documented that smiling is a universal and effective way to lift mood. But in the latest research on the power of the smile, researchers led by Marcus Munafo of the University of Bristol in England found that even seeing smiles on the faces of others can have a profound effect on a person's tendency toward violence or aggression — that is, as long as that person recognizes the smile as one of happiness, and not as a sneer (讥笑)． Munafo and his colleagues conducted a series of experiments involving normal adults and highly aggressive teens referred to a youth program, 求值:=________．