Novelist Agatha Christie used words that invoked a chemical response in readers and made her books "literally unputdownable", scientists have said.
A neurolinguistic study of more than 80 of her novels concluded that her phrases triggered a pleasure response.
"Christie's language patterns stimulate higher than usual activity in the brain," Dr Roland Kapferer said.
Her grandson Mathew Prichard told The Times: "It's not really a mystery. She was simply a writer of great plots."
More than two billion Agatha Christie books have been sold
The Agatha Project study was carried out by scientists from universities in London, Birmingham and Warwick for an ITV1 documentary.
It involved loading Christie's novels onto a computer and analysing her words, sentences and phrases.
It aimed to explain the enduring popularity of the work of the late author, who created detectives Miss Marple and Hercule Poirot and wrote novels such as Murder on the Orient Express.
Peter Ustinov played Christie's character Hercule PoirotThe team found that common phrases used by Christie acted as a trigger to raise levels of serotonin and endorphins, the chemical messengers in the brain that induce pleasure and satisfaction.
These phrases included "can you keep an eye on this", "more or less", "a day or two" and "something like that".
"The release of these neurological opiates makes Christie's writing literally unputdownable," Dr Kapferer said.
Christie was also found to have used a very limited vocabulary.
"It means that readers aren't distracted and so they concentrate more on the clues and the plots," said Dr Pernilla Danielsson of Birmingham University.
They also found that Christie frequently used dashes to create "a faster-paced, unreflective narrative".
Christie is listed in the Guinness Book of Records as the best-selling author of all time and attributed with selling two billion books worldwide.
Dr Kapferer said: "Our next step is to seek to replicate these experiments with other leading authors to discover whether their writings cause similar neurological activity among readers."
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