According to a new study, male mouse tears contain a sex pheromone called ESP1, which makes female mice more receptive to mounting.

While sex pheromones are known to have similar effects in other animals, the new study shows for the first time how the interaction works "at the molecular level and also the brain level," said study co-author Kazushige Touhara of the University of Tokyo.

(Related: "Pheromone in Urine Spurs Mating in Elephants.")

Male mice shed tears to keep their eyes from drying out. As they groom themselves, the tears—and the pheromone—get spread around their bodies and nests.

When female mice come in contact with a male or