The title is based on the three witches' dialog in Shakespeare's 'Macbeth' (Act IV, Scene I): "Double, double toil and trouble; Fire burn and cauldron bubble."
In this episode, Jeanette Nolan plays a witch akin to one of Macbeth"s witches, hence the episode title's ("Bubble, Bubble, Toil, and Trouble") allusion to the witches scene in the famous Shakespeare play. Coincidentally, Jeanette Nolan had, in her film debut, played the starring role of Lady Macbeth opposite Orson Welles in the latter's 1948 film production of Macbeth.