He stood up straight and looked the world squarely in the fields and hills. To add weight to his words he stuck the rabbit bone in his hair. He spread his arm out wide. "I will go mad!" he annouced.

So you can imagine what happens when a mainland species gets introduced to an island. It would be like introducing Al Capone, Genghis Khan and Rupert Murdoch into the Isle of Wight - the locals wouldn't stand a chance.

'These things will become clear to you,' said the old man gently, 'at least,' he added with slight doubt in his voice, 'clearer than they are at the moment.'

Time, we know, is relative. You can travel light years through the stars and back, and if you do it at the speed of light then, when you return, you may have aged mere seconds while your twin brother or sister will have aged twenty, thirty, forty or however many years it is, depending on how far you traveled. This will come to you as a profound shock, particularly if you didn't know you had a twin brother or sister.

It is most gratifying," it said, "that your enthusiasm for our planet continues unabated, and so we would like to assure you that the guided missiles currently converging with your ship are part of a special service we extend to all of our most enthusiastic clients, and the fully armed nuclear warheads are of course merely a courtesy detail. We look forward to your custom in future lives ... thank you.

It's not the fall that kills you; it's the sudden stop at the end.

Six pints of bitter, said Ford Prefect. And quickly please, the world's about to end.