Researchers in the Seventies found that the rodent's ultra-sensitive nostrils could detect rises in adrenalin from sweat exuded by passengers at airport security checks. The experiment failed because gerbils could not distinguish between nervous terrorists and innocent travellers afraid of flying. But, as we learned yesterday, MI5's gerbil file still exists and there seems no reason why the methodology could not be refined. In an era of equality, rodents of both genders have a right to serve in the front line alongside prancing thoroughbreds.