This is a peculiar comic. It’s one of our old ones, and over the years many people have had a chuckle at it. When you ask them to explain what’s amusing about it, however, many people either can’t (“There’s just something funny about it”) or they go into a long and convoluted explanation of the joke, which turns out to be completely different from our own interpretation of it.
So I’m posting it with no commentary or pointers as to what the underlying joke is actually intended to be. If you find it funny, mildly amusing, or just like the cow, then whatever your interpretation of it that’s good enough for us. If you don’t “get it”, then it doesn’t matter – you can easily kill a good joke with a little analysis, so even if we did explain it, you still wouldn’t find it funny
'...and when you've finished, just give the secret code word, "MOO", and we'll come and cut you out...'