It seems a little strange to press on someone's belly to dislodge something from the throat, but the Heimlich maneuver is proven to be remarkably effective. It works by putting pressure on the diaphragm, which generally holds a lot of air. The thrusts force the air out of the diaphragm in sharp, explosive blasts, which is usually enough to propel the food back out of the choking person's throat.
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