Tha can carry a duck up t'mountain but tha can't mek it quack

Talking to a colleague in IT support about our People's Network computers. He's perplexed:

"They're all the same model and make of PC. They've all got the same software on them. In fact, they're all copies of the same image, so they should all be identical clones. But they're not, are they?"

"No," I reply.

"I can't understand it. Anyway, I've taken the picture of the bloke in his vest off the desktop on PC1 again. And I've turned the sound down on 2 and 5 again. And I've put the Flash plug-in back onto 6 again. And when I'm logged on I haven't been able to replicate that thing on PC 10 where the Word document's in portrait orientation right up to the point where it gets printed: how the hell it does that I don't know, it only happens to some of your customers. We've been talking about this back at the office: what would you say to our blitzing the whole lot one evening?"

"Fire bombing's a bit extreme isn't it?"

"That's not what I meant but I'll take it back as an idea."