We, people, typically think of ourselves as people. It can be jarring to remember that we're also mammals who, like most other mammalian species, unconsciously send odor signals to each other carrying information about our gender, our health, ourreproductive state, our mood, and even our potential to be a compatible mate. If the idea that your secretions say something about you creeps you out, then you won't welcome the news that the revealing scent signals we emit may actually be the end-products of microbial fermentations carried out in our bodies' damp, low-oxygen creases. A recent study of scent signals in hyenas presents the best evidence to date that bacteria are responsible for producing pheromones in a mammalian species. The implication of these results is that the bacteria in our underarms may have a surprisingly complex role in our social lives.