Experts in artificial intelligence have built a computer programme that can understand simple jokes, marking an important step in making robots friendlier to humans.Previous attempts at getting machines to understand humour have failed miserably, because what is funny to humans is subjective and complex and difficult to programme. But, Scientist of the University of Cincinnati in Ohio have devised a prototype joke-detection software.

They began by loading a programme with a database of words, extracted from a children's dictionary to keep things simple, and then supplied it with examples of how the same word can have different meanings depending on the context. When presented with a text, the programme uses that knowledge to work out how new words may relate to each other, and what they probably mean.

If it fails to find a word that matches its context, it rummages around in a digital pronunciation guide for similar-sounding words. And if any of those words are a better fit for the rest of the sentence, the passage is flagged, ha ha, as a joke. So far, the joke-bot only understands rather leaden puns and still delivers a blank look when facing more complex stuff or dead-pan humour.