It may not be considered manly for humans to cry. But when male mice shed a tear, they seem to be trying to prove their masculinity. So say Japanese researchers who have discovered that male mice release pheromones in the fluid that moistens their eyes. “Nobody expected that sex-specific pheromones would exist in tears,” says Kazushige Touhara of the University of Tokyo in Chiba. Pheromones, the chemicals that convey messages about everything from fear to sexual desire, are most common in sweat in humans, and in urine in mice.