Today tens of thousands of people run the Boston marathon amidst tight security. A year ago two bombs were detonated at the finishing line, killing three and injuring 260. Social media went into overdrive as people frantically pieced together clues which might lead them to the bombers. From this patchwork of evidence two suspects emerged and rumours began to spread. During the London riots in 2011 people tweeted photos of the London Eye ablaze. Rumours circulated that rioters had broken into the zoo and released wild animals. A tiger was even spotted prowling around in Primrose Hill; there was even a grainy picture to prove it. We seem to be spending less time verifying facts and more time believing things that fits in with what feels right. Is technology helping or hindering the flow of good information? Do we need to think before we retweet? In this episode of The Digital Human, Aleks explores how rumours spread both online and in the physical world and discovers how in the echo chamber of social media falsehoods repeat until they become truth. Contributors: Alexis Madrigal of The Atlantic, psychologist Nicholas DiFonzo, computer scientist Kalina Bontcheva, DJ Russ Gibb, Twiggy Garcia and Ty Evans. Producer: Caitlin Smith.