The "Shouldn't drink and horse" joke.
Not a great joke IMO. Just the wrong way to say it just to make a lame joke. That would be like a modern day person saying don't drink and car. Don't drink and ride would still be as *beep* a joke as don't drink and horse but would at least make more sense.
He's taking the knife out of the Cheese!
Do you think he wants some cheese?