Our hearts and prayers go out to all the families involved in the recent tragic school shooting in Florida. Are mass shootings contagious? Some scientists say 'yes' as heartbreaking as that might seem. Our guest Arizona State University Physicist and Research Professor Sherry Towers studies statistics around mass shootings and how many are inspired by previous shootings. From 2006 to 2017, there have been more than 350 mass killings in the United States.