Chicago PD's  Sophia Bush got a crash course in law enforcement for her role on the TV drama and was surprised by what posed the greatest challenge. "Learning to handcuff someone was so much harder than learning to shoot a giant M4 rifle," the star says, before offering to demonstrate her technique. With such tense story lines on the show, she admits the cast is often pulling practical jokes on each other. "It's not appropriate at all, but we need it!"