The dogs owner says, "How about double or nothing and I'll ask him something else." The bartender agrees and the owner turns to the dog and asks, "Who was the greatest ballplayer of all time?"
The dog answers with a muffled "RUD." With that the bartender picks them both up and throws them out the door.
As they bounce on the sidewalk the dog looks at his owner and says, "Ronaldinho?"
You have to understand that the dog barking sounds are similar to "ROOF" and "RUD" which are the answers of the two questions in the story. We first thought that the dog can't actually talk. The owner just prepare the questions that the real answers are similar with the barking sound.
However, we understand from the last sentence that the dog can actually talk when it asks the owner whether its answer should be Ronaldinho instead of Rud (Van Nistelroy).
Announce = To make known publicly
Bartender = It means have sex in the story
Muffle = A structure to put animals inside.
Sidewalk = Force other person to have sex with
Some sources from http://www.thefreedictionary.com