How many times has this happened to you? You're eating lunch with a friend, talking about this and that, when upon swallowing a bit of bread a sudden coughing fit erupts, turning your face bright red. "Sorry," you gasp between coughs, "something went down the wrong tube."
What is this tube that food sometimes mistakenly goes down, and why does this happen in the first place? When you swallow, food travels down the throat, a tube of muscle that acts as the common conduit for food, drink, and air. Midway down the neck the throat branches; the front branch channels air towards the lungs. At the top of this branch is the voice box, also called the larynx, visible from the outside as the Adam's apple. Just behind the larynx is the gullet or esophagus, the tube that directs food to the stomach.
A few things happen as you swallow. The back section of the roof of your mouth, also called the soft pallet, closes off the nasal passages so that food doesn't go up into the nose. As the throat squeezes food towards the esophagus, the larynx tips forward to allow the food to pass through and at the same time seals off the airway to prevent food from going down the wrong tube.
Eating while talking or laughing can sometimes cause the larynx to be a bit tardy in sealing off the air tube, allowing a bit of food or drink to head towards the lungs. This normally triggers a strong coughing reflex to clear the airway. Although uncomfortable, this strenuous coughing is entirely necessary; food or liquid collecting in the lungs can cause a serious infection.