A a couple (old man, young woman) go to a doctor.
"Doctor, my husband doesn't satisfy me any more."
The doctor thinks a bit:
"Ok, this is what you will do: Next time you have sex, get a young, handsome man, strip him of his clothes, and have him wave a towel at you while you are doing it."
The couple do that, but to no avail.
"Doctor, it didn't work, my husband still didn't satisfy me"
"Ok, this is what you do. Have your husband wave the towel, and let the young man have sex with you"
The couple do that, and the woman was completely satisfied.
After the job was done, the husband says to the young man:
"See? THAT'S how you wave a towel!"