Read the excerpt from “You are Old, Father William,” by Lewis Carroll. Identify the pair of lines that expresses a humorous tone.
"You are old, Father William," the young man said,
"And your hair has become very white;
And yet you incessantly stand on your head—
Do you think, at your age, it is right?"

"In my youth," Father William replied to his son,
"I feared it might injure the brain;
But, now that I'm perfectly sure I have none,
Why I do it again and again."