From Hitchcock's 'Rear Window' to Facebook and Twitter, from Soviet Spies to Parisian cafes, eavesdropping is a universal phenomenon. John Locke, who has provided the first serious and systematic study of the behaviour, tells Laurie that it is a practice which extends into the animal kingdom and brings advantages to birds and chimpanzees. An attempt to understand the lives of others can help one live better oneself but despite the fact that it has shaped human history and culture, listening in to what others are saying continues to have a very bad name.