A typical Prisoner's Dilemma (PD) game was used to compare the level of cooperation of dyads allowed to communicate before every other trial to that of dyads not allowed to communicate. Further, communication dyads were separated into high and low cooperative groups and the differences in the types of messages sent by each group were analyzed Communicative dyads exhibited significantly higher levels of cooperation that did no communication dyads. Moreover, high cooperative communicators evidenced the use of significantly different types of messages from those used by low cooperative communicators. Specifically, the high cooperative dyads used more messages categorized as "expression of positive effect or trust" and "coordinate joint choices;" and low cooperative dyads used more messages categorized as "ambiguous" and "expression of negative effect or distrust.".