Grammar is essentially a system of rules for taking a finite set of discrete elements and combining them into a limitless range of novel expressions. For humans, grammar cobbles together words to create sentences. There is no evidence that animals have a similar system to produce sequences of calls with more expressive meaning. Together with W. Tecumseh Fitch of the University of St. Andrews, Marc D. Hauser, professor of psychology and Harvard College Professor, exposed cotton-top tamarins to two novel grammars based on patterns of meaningless syllables. Following this initial exposure, the tamarins heard a series of recordings, some of them violating the rules of Hauser and Fitch’s grammars. When the animals perceived such inconsistencies, they tended to glance toward the speaker piping out the sounds, a behavior often used as an indicator of novelty detection in studies involving both animals and infants. Based on the percentage of the time the tamarins looked to the speakers, Hauser and Fitch determined that the animals were able to perceive violations of the simpler grammar but did not take note of infractions involving the more complex grammar. Their study was reported in the journal Science.