Hello and welcome to More or Less on the BBC World Service. We are your weekly guide

to the numbers all around us, and I'm Tim Halfard.

Michael Blastland is a broadcaster, author and, a long time ago, one of the creators of

More or Less. Yes, you can blame him for everything. He has a new book out. It's called

The Hidden Half, and it's all about the hidden causes and factors that influence the way

the world is, all the things we simply can't see, measure or understand.

You can be the rational, paragon of philosophers' dreams, you know, that model intelligence

and you will still not be able to catch this stuff.

He joined me to talk about some strange crayfish, economic productivity and counting sheep.

Are you right about counting sheep? So, tell us about the sheep. It starts with a picture

of sheep and a lamb in a field, and you say, all right, how many sheep? Maybe two, maybe

one. And then you say, well, I'm actually by the way, the U, because it's a U, I'm

making this up. But the U is pregnant. It's a very pregnant. About to give birth in the

next couple of minutes. Right. How many sheep? So, maybe one, maybe two, maybe three.

Maybe two and a half or maybe one and a half and a quarter or something like that. Anyway,

counting to three just got difficult. And actually this is what we're always showing here

is that there's a simple, definitional problem whenever you count anything. You've got to say,

are you counting the same things? Because if this thing isn't sufficiently like that thing,

then do you say there are two of them? Or do you say there are one of those and one of

those? And you might have different purposes when you're counting them. If you're counting

sheep and lamb, if you're thinking about the meat, you might say one. Because that's the

only one you can send to slaughter now. So, the time of the year that you count them and

...