"Father William" belongs to Lewis Carroll. HP belongs to J.K.Rowling. I only own this poem. This poem takes place in the future, and it was a bit funnier to think of Snape as the weird one.

"You're old, Professor Snape," 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," Professor Snape replied to Lucius Malfoy's son,
"I feared that it might injure the brain;
But now I am perfectly sure that I have none,
Why, I do it again and again."

"You're old," said Draco, "as I mentioned before,
And have grown most uncommonly thin;
Yet you turned a back somersault in at the door-
I thought that you thought it was a sin!"

"In my youth," said the greaseball, as he shook his white locks,
"I kept all my limbs very supple
By the use of this potion- ten sickles the box-
Allow me to sell you a couple."

"You are old," said Draco, "and your jaws are to weak
For anything tougher than suet;
Yet you finished the hippogriff, with the bones, the talon, and the beak-
Pray, how did you manage to do it?"

"In my youth," said the professor, "I took to teaching,
And talked until the bell's chime;
And the strength in my jaw, a higher point reaching
Will last the rest of my time."

"You are old," said the youth, "one would hardly suppose
That your eye was a steady as ever;
Yet you balanced a flobberworm on the end of your nose-
What made you so awfully clever?"

"I have answered three questions, and that is enough,"
Said the professor, "don't give yourself airs!
Do you think I can listen all day to such stuff?
Be off, or I'll curse off your hair!"