Have you ever watched any of the "Winnie the Pooh" series put out by Walt Disney? There is a character in there that is a ground hog. He does all the contract excavating for anyone who needs a hole dug.
He has a "whistle" when he talks. It happens everytime he uses an "s" word. The tounge doesn't make the ssss sound but a whistle sound.
Now to make it really funny, add the voice characteristics of Mr. Haney on Green Acres to the whistle and you got a combination that will get you rolling!
Very difficult to do when you try it deliberately but funny when done right.