The canonical test sentence for machine translation software. However, don't bother: even the crappiest MT program will almost certainly have a smart response hard-coded. It contains several varieties of structural and lexical ambiguity which make mechanical parsing difficult, but any English speaker, or at least any English speaker who has not spent too much time programming in Prolog, will instinctively understand it - in the absence of any particular contextual information - as a simplistic simile about the passage of time; a prime example, therefore of the NLP problems with real-world knowledge.