I was afraid of something like that. Well, Asimov had some other groaners, he’s not off the hook. 
Oh, he’s not off the hook. He didn’t add groaners to his fiction, as far as I know. But he wrote three books of Lecherous Limericks. I imagine there were a few puns in his anthology introductions and his autobiographies.
It’s been awhile.
Why do ducks have webbed feet?
To stamp out fires.
Why do elephants have flat feet?
To stamp out burning ducks.
How many dull people does it take to change a light bulb?
One. (should be delivered as deadpan and monotone as possible)