I probably found this on Usenet once.
There are two lions in the zoo. One says "You know, I am completely fed up with being here. Tomorrow, I intend to make my escape. The other says "I agree. I shall do the same". The following day at feeding time, they overpower their keeper, leap out of the cage, and run into the park outside the zoo. As they part, the first lion calls "Let's meet in six months' time. We'll come back to this park, and tell each other how we got on". Then they go their separate ways.
Six months later, as arranged, they meet. The first lion says "Well, here we are. But say, what happened to you??? Your fur is falling out, you've got a torn ear and scratches everywhere, you're terribly thin — you look terrible". The second lion replies "When I left the park, I ran towards the centre of town. There are a lot of butchers' shops there, and I thought I'd easily be able to overpower the staff and drag off a joints of meat. So I ran into one of the shops, but the owner called the police, and they called the army, with lots of men with nets and guns, and I only just got away. I managed to hide in the woods outside town, and since then, I've been living a miserable existence eating berries and the occasional rabbit when I can catch it, and I think it would be better to go back to the zoo. But say, you look as though you're OK. Youre fur is sleek and glossy, you're well-fed — what happened?
And the first lion says "You know there's an science park over at the other side of town. It's full of bushes and shrubs, and I decided to run over there and use it as my hideout. Well, there's an IBM software office there. So I've been hiding out in the bushes, and I just eat an IBM manager each day. It's great. There's an endless supply, and no-one notices when one's gone.