Female mice that are heavily pregnant or have recently given birth produce a banana-smelling chemical in their urine that stresses out males, possibly to stop them from killing their pups.

Jeffrey Mogil at McGill University in Montreal and his colleagues discovered this behaviour by accident. “We were doing experiments with pregnant female mice and noticed that male mice that were being used for other experiments in the same room were acting a bit crazy,” he says.

— Read more in Female mice release banana-scented urine when pregnant to deter males at New Scientist.