To Gulp Without Chewing (Swallow)

Lyrics

On the left, Diagram A.
On the right, Diagram B.
The subject is a single word with two distinct applications.
Let us begin.

Diagram A: *Hirundo rustica*. The Barn Swallow.
Observed by John James Audubon, circa 1838.
He noted its swiftness, its sudden turnings.
A forked tail cutting the dusk at 7:30 PM.
Its nest is a cup of mud and straw, high in the rafters.
It performs what is called "aerial drinking."
Skimming the surface of the pond, beak open, it takes in water without landing.
It consumes mosquitoes. It migrates.
This is the noun.

Swallow.
Noun: A migratory passerine bird of the family Hirundinidae.
Swallow.
Verb: To cause or allow something, especially food or drink, to pass down the throat.
Note the distinction.

Diagram B: The pharynx.
Illustrated in Gray's Anatomy, 1858 edition.
Here is the epiglottis, a flap of cartilage.
Here is the esophagus, the muscular tube.
The action is a complex neuromuscular reflex.
I will demonstrate with this glass of water, currently at 72 degrees Fahrenheit.
The bolus moves, the larynx rises, respiration is inhibited.
It is an involuntary act, once initiated.
This is the verb.

Swallow.
Noun: A migratory passerine bird of the family Hirundinidae.
Swallow.
Verb: To cause or allow something, especially food or drink, to pass down the throat.
The two are not to be confused.

One action takes place in the open air, a flash of blue against the clouds.
The other, in a dark, internal passage.
One is a freedom of flight.
The other, a necessity of biology.
The bird swallows its food on the wing.
The throat swallows the food that sustains the body that observes the bird.
A closed loop. Symmetrical, in its way.

Diagram A. Diagram B.
The noun. The verb.
One an object in motion.
The other a motion of an object.
The lecture is concluded.