After eight people were killed at a Travis Scott concert in Houston late Friday, many of us were left wondering: How did this happen? An expert on crowds explains how too many people packed closely together can become deadly.Read more:An estimated 50,000 people attended the sold-out 2021 Astroworld Festival at NRG Park to see Travis Scott, whose concerts have a reputation for being raucous.The Washington Post reviewed dozens of videos from the night to understand how the concert became a mass casualty event, synchronizing video from the audience with a live stream of Scott’s performance published by Apple Music. The videos show a chaotic scene, with concertgoers crying out for help as the show continued, the loud music drowning them out.The crowd surge victims include a 14-year-old who loved baseball, two friends celebrating a 21st birthday and a 27-year-old attending the concert with his fiancee. Here’s what we know about the victims.We reached out to Keith Still, a professor of crowd science at the University of Suffolk in Britain, to talk about how these tragedies happen and how they could be prevented.If you value the journalism you hear in this podcast, please subscribe to The Washington Post. We have a deal for our listeners: one year of unlimited access to everything The Post publishes for just $29. To sign up, go to washingtonpost.com/subscribe.