One of the human body’s most notorious limitations is the way your feeding chute (your esophagus) passes just over your breathing tube (the trachea). A flap of cartilage called the epiglottis closes over your airway when you swallow to prevent food from slipping in. The problem is that the epiglottis isn’t foolproof. If you cough or try to talk while eating, you can force your epiglottis open. With bad timing and the wrong food, you can end up blocking your airway completely.
Life-threatening choking is distinctive: Silence is the most obvious symptom. Because people use the same passageways to breathe and talk, someone with a complete airway obstruction will be almost completely unable to speak, gurgle, cough, or wheeze. You know what comes next—the Heimlich maneuver (also known as abdominal thrusts), as you’ve seen in countless television movies. But don’t act yet, because modern first-aid procedures suggest this sequence:
• Encourage the person to try to cough.
• Slap the person’s back 5 to 20 times, using the heel of your hand. The goal is to create vibrations that can dislodge an obstruction.
• Now it’s time for abdominal thrusts—a risky but potentially life-saving move. Stand behind the person and wrap your hands around his abdomen, just above the belly button. This is where you’ll find the diaphragm, the muscle that sits just under the lungs and controls breathing. Make a fist with one hand, and wrap your other hand around it. Then pull your fist upward and inward, forcefully. You may need to repeat the move several times. Done right, abdominal thrusts increase the pressure in the lungs and hopefully blow out the lodged object. (They may also bruise the abdomen and fracture a rib.)
Source of Information : Oreilly - Your Body Missing Manual