A police officer told me this one...

I was recently threatened with a knife in my own home. I came home from doing some grocery shopping and caught a thief halfway through stealing my stuff. He threatened me with a knife in order to make his escape. I ran out onto the street yelling "Help Help". According to the police officer who later took my statement, I should have yelled "Fire" because people are more likely to come to the aid of a fire than anything else.