the harry potter books have sold more than 450 million copies and its success may lie in the use of words used - rather than the texts as a whole .
by scanning the brains of people reading passages from the collection , researchers discovered that the common use of ` arousing words ' affected parts of the brain concerned with emotion .
the emotional potential of words is rated in terms of valence and arousal ratings that can be categorised as negative , neutral , and positive .