eLife Assessment
This is a valuable study that tests the functional role of food-washing behavior in removing tooth-damaging sand and grit in long-tailed macaques and whether dominance rank predicts level of investment in the behavior. The evidence that food-washing is deliberate is compelling and the evidence that individual investment in the behavior varies is solid. Overall, the paper should be of interest to researchers interested in foraging behavior, cognition, and primate evolution.