‘But I still don't understand about the tortoise,’ he said, with some difficulty. He'd just taken his first mouthful of Ephebian wine, and it had apparently varnished the back of his throat.

‘'S quite simple,’ said Xeno. ‘Look, let's say this olive stone is the arrow and this, and this-’ he cast around aimlessly - ‘and this stunned seagull is the tortoise, right? Now, when you fire the arrow it goes from here to the seag - the tortoise, am I right?’

‘I suppose so, but-’

‘But, by this time, the seagu - the tortoise has moved on a bit, hasn't he? Am I right?’

‘I suppose so,’ said Teppic, helplessly. Xeno gave him a look of triumph.

‘So the arrow has to go a bit further, doesn't it, to where the tortoise is now. Meanwhile the tortoise has flow - moved on, not much, I'll grant you, but it doesn't have to be much. Am I right? So the arrow has a bit further to go, but the point is that by the time it gets to where the tortoise is now the tortoise isn't there. So, if the tortoise keeps moving, the arrow will never hit it. It'll keep getting closer and closer but never hit it. QED.’