I second that! The airport environment has close to zero tolerance now in terms of what people are carrying, and where and how people try to smuggle-in contraband, and rolls of film have been on the radar for a while now. If Customs want to unravel a roll of film, there is nothing stopping them (least of all you!) — the law is on their side and they are entitled to be very thorough if they have the slightest suspicion. Just put everything on the counter as directed and in through x-ray: keeping things nice, pleasant, civilised and orderly will make everybody's day; the reverse having you shunted off for an intricate interview in a back room (and yet more things pulled apart). All this is because at some stage idiots have smuggled in drugs in otherwise innocuous-looking rolls of film (opening the canisters, removing the film spool, stuffing in e.g. heroin or ice). It is through the refined detective work of Customs that we don't have a great deal of illicit stuff getting through the border, and their methods and detections are always being fine-tuned.