This is by no means mine, but I figured it's worth sharing. Terry Pratchett's take on the traditional Riddle of the Sphinx:
What goes on four legs in the morning, two legs at noon, and three legs in the evening?
[SBLOCK]‘Let’s say for example that the average life expectancy is seventy years, okay?’
‘Okay’ said the Sphinx, in the uncertain tones of someone who has let the salesman in and is now regretfully contemplating a future in which they are undoubtedly going to buy life insurance.
‘Right. Good. So noon would be age 35, am I right? Now considering that most children can toddle at a year or so, the four legs reference is really unsuitable, wouldn’t you agree? I mean, most of the morning is spent on two legs. According to your analogy … only about twenty minutes immediately after 00.00 hours, half an hour tops, is spent on four legs. Am I right? Be fair.’
‘Well—’ said the Sphinx.
‘By the same token you wouldn’t be using a stick by six p.m. because you’d be only, er, 52,’ said Teppic, scribbling furiously. ‘In fact you wouldn’t really be looking at any kind of walking aid until at least half past nine, I think … I’m sorry, it’s basically okay, but it doesn’t work … You just need to alter it a bit, that’s all.’
‘Okay’ it said doubtfully. ‘I suppose I could ask: What is it that walks on four legs—’
‘Metaphorically speaking,’ said Teppic.
‘Four legs, metaphorically speaking,’ the Sphinx agreed, ‘for about—’
‘Twenty minutes, I think we agreed.’
‘—okay, fine, twenty minutes in the morning, on two legs—’
‘But I think calling it “in the morning” is stretching it a bit,’ said Teppic. ‘It’s just after midnight. I mean, technically it’s the morning, but in a very real sense it’s still last night . .. Let’s just see where we’ve got to, shall we? What, metaphorically speaking, walks on four legs just after midnight, on two legs for most of the day—’
‘—barring accidents,’ said the Sphinx, pathetically eager to show that it was making a contribution.
‘Fine, on two legs barring accidents, until at least suppertime, when it walks with three legs—’
‘I’ve known people use two walking sticks,’ said the Sphinx helpfully.
‘Okay How about: when it continues to walk on two legs or with any prosthetic aids of its choice?’
The Sphinx gave this some consideration.
‘Ye-ess,’ it said gravely. ‘That seems to fit all eventualities.’[/SBLOCK]
