I first heard this joke in 1974.
It's in a scene from the Movie,"Alice Doesn't live here Anymore".A Very young Jodie Foster tells it differently,replacing the Bear with a Gorilla & a Gorilla extractor.
She ends it with the extractor,after falling out of a tree,running away with his hands over his Groin yelling,
"SHOOT THE DOG!,SHOOT THE DOG!,SHOOT THE DOG! 