Joke for Grammarians

[slightly off-color joke to follow]

Harry is getting older, and find that he is unable to...ahem...perform to his satisfaction. Visits to his doctor result in pills and such, but nothing works. Finally, desperately, Harry seeks the help of a local witch doctor.

After much chanting and smoke and incantations, the witch doctor tells Harry, "This is a very powerful spell, so it will only work once every year. Just say '123' and you'll have an erection for as long as you like!"

Harry is very pleased "What about when it's over, and I don't want to continue?"

"You or partner just have to say '1234' and it will go down. But remember--you can't try again for another year!"

Harry rushes home, eager to try the new spell. He spiffs himself up, shaves, uses his best cologne, and climbs into bed next to his wife. Putting his hand lovingly on his wife's shoulder, he whispers, '123' and suddenly is more aroused than he has ever been in his entire life! It worked! Just like the witch-doctor promised!

His wife rolls over sleepily, and asks, "Harry? What did you say 123 for?"

And this, dear readers, is why you never end a sentence with a preposition.