The witches from Shakespeare's play, Macbeth. This is the chorus while they are dropping ingredients into their cauldron.
it means that trouble is coming this way. look it up in harry potter lyrics for double double toil and trouble, and you'll get your answer.
It was supposed to be a "spell" they were doing.
MacBeth
It's a very famous monologue in Shakespeare's Macbeth, spoken by the Three Witches.
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