So I brags, "...in fact, my dog's prob'ly faster than that sportscar of ur'in."
"You're on!" says Him speeding away. But amazed and distracted by my hound keepin' up, he slams a post. Shakin, but comin' to, he says, "Sure was a fast dog, but where is he ?"
"There", I point.
"Not" says He, "That dog, wer'nt wearin' a red collar."
"Collar ? Hell," says I. "Thats his pooper! He's not used to stoppin' quite that fast !"

I don't get it...

I don't really either. I think maybe we're supposed to assume the dog stopped when the car did?

[lil mutt]

i didnt get it also.. gonna read it again later...