Now, sir, your coat is off!
And see–
Your right-hand pocketed!
So let it be:
While o’er your arm
An endless string–
Some three yards round–
Hangs like a sling.
Take the string off–
But, just for fun,
It must be done
Keeping your right-hand in its place,
And not a smile must stir your face.
Until you find this puzzle out,
No coat shall wrap your back about.

How is it to be done?