What rhetorical device does Twain use by referencing this well-known proverb

Even though the proverb was not posted here, this question is still perfectly answerable.

The rhetorical device Twain uses by referencing a well-known proverb is allusion.

Explanation:

Allusion is a figure of speech in which a reference is made to something or someone that has significance. The author does not explain much, since he/she assumes the audience knows who or what he/she refers to.

For instance, if someone says a woman is as beautiful as Helen of Troy, we would understand he/she means that woman is extremely beautiful. Helen of Troy is a famous character from the Iliad, by Homer, and she was the most beautiful woman in the world. The person making the allusion will not explain this fact, since it is well know.

Therefore, if Twain is referring to a well-known proverb, he is making an allusion to it.

either a donut or a sphere or a pancake or a flat sphere. it depends on where the vertical line is.

if the line goes through the center of the circle and is perpendicular to a diameter containing the center, then you get a flat circle.

if the line and the diameter of a the circle meet in the center of the diameter and at an angle, you get a pancake.

if the line is on the circumference of the circle and is at right angles   to the circle you get a ring.

if the line contains the diameter, you get a sphere.

the the line is parallel to the diameter and touches the circumference, you get a donut.

what sentence

explanation: