An allegory is the occurence of the same letter or sounds in a string of closely connected words. The sentence shows a pattern that is allegorical.
This can be seen in the use of stern, and sad which both begin with S. The next group of words which are darkly meditative, distrustful, and desperate, all begin with the letter, d. They also have similar sounds.
Fast food is convenient because it is cheap and it’s prepared ahead of time and you don’t need to cook it. You just order and enjoy the meal especially if you don’t know how to cook. It saves time and energy.