Since the Charlie Hebdo attacks in January, from which 16 people died, Paris-area ambulance crews and emergency personnel have taken part in regular exercises designed to test their readiness for possible attacks. One such exercise was held on Friday morning, the day of the latest terror attacks. In a twist of fate, the simulated emergency was a mass shooting, according to Dr. Mathieu Raux, emergency room chief at the Pitié-Salpetrière hospital in Paris.