Novelist Agatha Christie used identifiable patterns of words that made her books "literally unputdownable", researchers have said.
More than two billion Agatha Christie books have been sold
A linguistic study of more than 80 of her novels concluded that a number of key phrases triggered a pleasure response in readers.
Study co-ordinator Roland Kapferer said the researchers believed Christie's language patterns "stimulated higher than usual activity in the brain".
Her grandson Mathew Prichard told The Times: "It's not really a mystery. She was simply a writer of great plots."
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.
The team attributed this to common phrases including "can you keep an eye on this", "more or less", "a day or two" and "something like that".
Peter Ustinov played Christie's character Hercule Poirot
Mr Kapferer said they believed responses to these phrases would make Christie's writing "literally unputdownable".
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.
The Agatha Christie Code will be on ITV1 on 27 December.