Cheney and Seyfarth describe how one day the dominant male in the group of vervet monkeys they were studying noticed a strange male hanging around in a neighbouring grove of trees The strangers intentions were quite obvious he was sizing up the group in order to join it If he succeeded it was more than likely that the incumbent male would be ousted from his position of privilege With the vervet equivalent of a stroke of genius the male hit on the ideal ploy to keep the stranger away from his group As soon as the strange male descended from the grove of trees to try to cross the open ground that separated his grove from the one in which the group was feeding he gave an alarm call that vervets use to signal the sighting of a leopard nearby The stranger shot back into the safety of his trees As the day wore on this was repeated every time the stranger made a move in the groups direction All was going swimmingly until the male made a crucial mistake after successfully using the ploy several times he gave the leopard alarm call while himself nonchalantly walking across open ground