joke explanation - cows, horns...

[Lenka]

Joke: "Why do cows have horns? Because their horns don't work!"

I hope you won't consider me being stupid because I don't understand the joke... . What is the point? Maybe I can't understand it because of the fact that some of the words, e.g. "horns", have more than one meaning...
I' probably a little slow-witted as I really can't find the funny point of the joke!
Or is it one of the jokes that don't have any funny point and that's what makes them funny?

[Lenka]

In addition, cows (female) don't have horns...

[BobK]

The problem is, you've heard the wrong form of the joke. The question is 'Why do cows have bells?' Geddit?

b

[Lenka]

The problem is, you've heard the wrong form of the joke. The question is 'Why do cows have bells?' Geddit?

b

Ahhh! I see! Thanks, Bob!

(I assume that the joke is based on the second meaning of a horn (a musical instrument), right?)

[BobK]

(although I'd've picked a less tuneful sort of horn - a car horn (sometimes called a 'klaxon'). And the joke is also based on a double meaning for bell [=indicator of presence, as for example worn by a cow|generator of warning sound, as for example mounted on a bicycle's handlebars]

[Lenka]

Thanks!

[BobK]

You're welcome.

You could make the joke more biologically sound by making it:

Q Why do cows have bells?
A Because they don't have horns.

(I'm not sure of the biology. Aren't there some breeds that do, or am I just being a dumb townie?)

b

[Lenka]

Yes, there are a number of breeds where the females have horns. (Scottish Highland Cow, US Longhorn Cow.)
The males generally have bigger horns, though.

Oh, I should feel ashamed I didn't know that!