People who tend to hold favorable beliefs about revenge and engage in vengeful behavior are more likely to be neurotic, introverted, hostile, ruminative and predisposed to dwell on slights and transgressions, according to a new study by Robert A. Emmons, an associate professor of psychology at UC Davis. Those who tend not to favor revenge are likely to be extroverted and agreeable, he says. Subjects completed a questionnaire about their past vengeful behavior and wishes, as well as other scales measuring different aspects of their personality. Since vengeful impulses are related to personality traits that have been linked with physical ailments, such as hostility and anger, they may have health consequences as well, says Emmons. However, even though revenge often is cited as a motive for murder, rape, arson, adultery and other acts, it is not necessarily inherently irrational and destructive, he says. Emmons believes that some types of revenge can have positive consequences, such as prodding a person to higher achievements, and that the distinction between productive and non-productive expressions of revenge should be explored more thoroughly.