The history of science is one chock-full of mice and men. Historically, biological and medical research has largely depended on rodents, which provide scientists with everything from cells and organs to behavioral data. That's why a new study in which researchers found that mice actually fear men, but not women, has the potential to be so disruptive. It might mean that a number of researchers have published mouse studies in which their results reflect this male-induced stress effect — and they know nothing about it. In the study, published today in Nature Methods, researchers used the "mouse grimace scale" to measure pain responses in rodents exposed to men, women, or their respective smells. Pain is a proxy for stress because stress can, to a large extent, numb pain. So when the mice were confronted with the smell of men, they experienced less pain, whereas the presence of women — or their smell, Mogil says — "did nothing at all."