How would you like to have been born without any ability to feel pain? There are such people. One of them is being studied by doctors at a hospital in New York City. He is a 22-year-old clerk who really does not know the meaning of pain. But he wishes he did. Not long ago a packet of matches flared up  in his hand. Luckily the burn was not serious. It caused large blisters  but still did not bother him. He said the burn felt like a fly crawling(......) on his fingers. It has been the same story as far back as he can remember. He has never had headaches or sore  muscles. Bee stings, cuts and bruises  do not hurt. Being free from pain is not as wonderful as you may think. The young man has had to have rotted teeth pulled because he never felt toothache warnings. A sudden attack of appendicitis  could be deadly. Life without pain is as risky as trying to run a cruise ship without fire alarms. In the final sentence, the writer uses "fire alarms" to mean   _  .
loud noises that a person hears a signal that something is wrong heat warnings the ability to smell smoke