sling and dressing

Webにあった次ぎの話には過去に私がブログで取り上げた単語が二つも含まれているので、復習を兼ねて取り上げます。実話だそうですが、私にはジョークとしか思えません。
A woman received a nasty burn to her hand and needed hospital treatment. This meant she had to wear a large dressing and have her arm in a sling. She visited the hospital on a regular basis. The doctor would look at her wound and then write on a card what the dressing nurse had to do. The card was sent into the next room with the woman and was handed to the nurse who carried out the instructions.
As time went by the wound was healing nicely and the dressing reduced in size and the sling was no longer necessary. The dressing was getting to the point of being very small and the woman thought that her next appointment would probably be her last or next to last.
When she arrived at the hospital there was a new doctor in the surgery and he examined the wound. The woman went to the next room where the nurse gave her an even smaller dressing but insisted that the woman should wear a sling.
" I can't wear a sling! I drove here - I won't be able to drive home."
The nurse insisted that she was only carrying out what was on the card.
The woman continued to protest and demanded that the nurse check it with the doctor.
Eventually the nurse agreed and went into the surgery. A few minutes later the nurse returned and was very red faced.
"It's a new doctor," she said, "and his surname is Ling and his first name is Stephen - he just signed the card S. Ling."
The woman laughed when she heard but then turned to the nurse and said, "How many people have you sent out of here with a sling?"
"All of them." was the embarrassed reply.