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."
The scene in which Serena (as Samantha) makes a pass at Larry is interesting in that David White and Elizabeth Montgomery played lovers in The Rusty Heller Story (1960) starring Robert Stack.
This is Serena's second appearance (the first being on And Then There Were Three (1966)) and her first time in a color filmed episode. She will wear her mod hat and glasses again on Hippie, Hippie, Hooray (1968).
The closet in the kitchen is MUCH bigger than it should be and it includes a freezer. In other episodes, the door opens into a small broom closet or a stairway to the cellar.