“I heard this from my friend, Ryan. And it’s a joke that his father apparently used to tell, that he wasn’t usually taken in by.  But, the one version, of the joke that he was taken in by.

His father went on a trip to Texas with his uncle, uh, and his father was telling him, “oh you know, we went to this restaurant that was, basically right on a ranch, uh, and so, you know, there were all these cowboys around with their horses and we went into the restaurant and sat down and we were just eating. Uh, and then, this cowboy comes through the door, and, and you know, sits down and he’s actually leading his horse after him, into the bar! And so the horse walks up to the bar, and the bar tender says, “hey, why the long face? It was the only version of the joke that ever took my friend Ryan in.”

The phrase “why the long face,” is often seriously ask about a person’s emotional state; their face appears to be ‘long’ due to a frown and/or downcast expression.  In this case, Claire’s friend’s father tells the joke often.  But the only time Ryan ever found the joke amusing was when his father used it in a literal context.  The joke, “why the long face,” being asked of a horse takes the phrase literally as a horse’s face is physically long in structure.  It is amusing because the joke uses a normally innocuous phrase, but with the addition of an actual horse, or at least an imaginary horse, the entire meaning of the phrase changes.  Asking a horse why its face is long is a bit odd.  In addition, the idea that a horse is at a bar is even more ridiculous.  Consequently, imagining a bartender asking a horse why its face is long makes for an amusing joke. 

The frame of the joke, “A —— walks into a bar,” is widespread.  Commonly, horses and men feature in this type of joke.  But occasionally a giraffe, mushroom or Charles Dickens are the subject of the joke, with their own specific comeback.  Even inanimate somtimes walk into the bar (soccer balls, books).  The ability to modify the joke so easily lends itself to much interpretation and manipulation and is consequently spread rapidly and in multiple forms.

Annotation: Encyclopedia of Humor. http://www.smilespedia.com/a-guy-goes-into-a-bar/