The various snippets and teasers in the trailer for Series Nine have generated plenty of speculation and interest in the forthcoming new adventures of the Doctor and Clara: Was that a 1960s dalek in the background? Surely that's Karn - so does that mean 1976 villain Morbius is back? Was that a war torn Skaro - with biplanes? All interesting observations, but it is the identity of Maisie Williams' character that has generated the most chatter in fan circles. The line "What took you so long, old man?" has created a frenzy of theories as to her identity (Susan, the Doctor's daughter Jenny, Lorna Bucket etc.), even if in all likelihood she is an unknown character yet to be introduced. Whether it's a deliberately provocative throwaway line, a blooper, double entrendre, a teaser or a myth buster, fandom often gets embroiled in lengthy debates about a single line of dialogue. No doubt, the producers rub their hands in glee at the publicity - either that or face-palm because something which really shouldn't matter much in the general scheme of things has caused such consternation. Here's a rundown of some of the most talked about one liners - some are more controversial than others, but each of them seems to have taken on a life of their own, at times even at the expense of the story in which they feature.