What do prime ministerial pets teach us about politics? “Sex, Lies and the Ballot Box”, a new book edited by Philip Cowley and Robert Ford, two political scientists, contains some revealing polling. Shown a photo of Humphrey the cat, chief mouser at Downing Street over three premierships, voters reacted differently depending on the reported identity of his owner. Conservatives preferred “Margaret Thatcher’s cat”; Labour ones liked him better if they were told that he belonged to Tony Blair. (American researchers found those hostile to Barack Obama disliked his dog, too.) As Mr Ford puts it, voters lean on things they do know when deciding about things they do not. Bad news for unpopular politicians with great new policies.