Comments about the “little trap door” are accurate, but there’s an entirely different principle at work here. Namely, that the sucking motion created in drawing air into your lungs and the sucking motion created to draw liquid into your mouth are entirely different.
When you suck in air through a straw, your diaphragm is contracting and bowing towards your feet. This creates a partial vacuum in your lungs into which air flows.
When you suck in liquid through a straw, you are again creating a partial vacuum, but this time with an entirely different part of your body. The liquid sucking action is created by drawing your tongue into the back of your mouth. This creates a partial vacuum in your mouth into which liquid flows. At this point you then swallow, which is where the epiglottis comes into play.
To prove to your nephew that that the liquid sucking motion is entirely divorced of his lungs, have him do these two simple experiments:
Have him suck liquid through a straw while he holds him breath. Or better yet, have him suck liquid into his mouth while he blows air out his nose. Piece of cake, right?
Have him put a straw in his mouth and stick his tongue way out underneath the straw. Have him make a tight seal around the straw (this will be difficult with his tongue hanging out, but possible. Barely.) and have him grab hold of his tongue tightly. Now have him suck some liquid. He will feel his tongue trying to pull back into his mouth to create the sucking motion.
See? Lung sucking and mouth sucking are two entirely different things! Next week on “Fun With Your Body,” we’ll learn how, if muscles only contract, it’s possible to stick your tongue out!
~ Complacency is far more dangerous than outrage ~