You should call the police if someone is injured.
Kim sees someone in the street get hit by a car which drives away.
Kim wants to decide if she should call 911.
Kim calls 911 on her phone right away to help the injured man.
Kim walks away assuming someone else will call the 911.
An ambulance arrives to help the injured man 3 minutes later.
Everyone else does the same thing as Kim and the injured man gets no help.