"I think it (the fatwa) was very important to Christopher [Hitchens] in his thinking and in his politics...And so he became very exorcised and therefore very available to me during that time."To exorcise is to expel, drive out, cleanse--often with the help of a religious shaman, or a priest played by Max von Sydow. One definition of exercise, however, according to the American Heritage Dictionary, is "to stir to anger or alarm; upset" and I think that's obviously the meaning--and the word--Rushdie had in mind here.
Bonus Unintended Meaning Quibble: A headline on the Huffington Post today, about a fight for a soon-to-be-available front row seat at White House press conferences, reads: Bloomberg: We Deserve Helen Thomas's Seat, Not Fox News.
Nobody deserves Fox News.
