Scientists have found that rodents feel 36% less pain when a male researcher is in the room versus a female researcher. The rodents are also less stressed-out. The effect appears to be due to scent molecules that male mammals (including humans, dogs, and cats) have been emitting for eons. The finding could help explain why some labs have trouble replicating the results of others, and it could cause a reevaluation of decades of animal experiments: everything from the effectiveness of experimental drugs to the ability of monkeys to do math. Male odor could even influence human clinical trials.