Twain does not tell the frog story himself. He hands it to a rambling old man, Simon Wheeler, and reports Wheeler telling it. A story with a story inside it is a frame narrative. The comedy lives in the gap between the impatient narrator and the earnest teller. The reader has to sit there and listen too.

Deadpan means telling something absurd with a completely straight face, as if it were ordinary. Wheeler “never smiled, he never frowned.” He thinks the tale is important. He is not joking. That gap between how ridiculous the material is and how seriously the teller takes it drives the humor.

A tall tale exaggerates until it is impossible, then keeps a straight face. Twain escalates on purpose. A wheezing mare wins by coughing across the line. A sad bull-pup wins by one stubborn grip. A frog, after three months of training, out-jumps any frog alive. Each claim gets more ridiculous, but Wheeler reports each one as plain fact. Deadpan and escalation are the same joke working together.

A stranger loads Dan’l with a teaspoon of shot while Smiley hunts a rival frog. The champion cannot move. But the con is built before the shot is poured. The stranger has no frog, so Smiley offers to go catch one. That gets Smiley out of the way and gives the stranger time alone with Dan’l. A good joke prepares the reader to recognize the ending when it comes.