" Several sellers of hot meat pies and sausages in a bun had appeared from nowhere and were doing a brisk trade. [Footnote: They always do, everywhere. No-one sees them arrive. The logical explaination is that the franchise includes the stall, the paper hat and a small gas-powered time machine.] "

― Terry Pratchett , Wyrd Sisters (Discworld, #6; Witches #2)