Final answer:
The red-headed boy's boast of jumping high is humorous due to the ironic juxtaposition with a trained jumping frog's abilities, highlighting the boy's naïveté and creating a comical effect.
Step-by-step explanation:
The humorous scenario where the red-headed boy boasts about his jumping ability is derived from the context of Mark Twain's story where a frog, trained to jump high, is the central figure.
The boy's claim is ironically amusing in light of the frog's exceptional jumping skill, as humans typically cannot jump anywhere near as high as a well-trained frog.
It is also funny because the boy is unaware of the intensive training the frog has gone through to achieve such jumping prowess, making his boast seem naïve and comical in comparison.