4 ideas
Dorothy finds a copper man locked in a rock chamber in Ev. Throughout the adventure he stops mid-sentence or freezes mid-action whenever one spring runs down, and the others must rewind him before he can continue.
Tik-Tok's thought, speech and motion run on independent springs, so one faculty can fail while the others keep working. This separates producing fluent language from understanding it, and makes a machine's competence depend on which component is currently energized.
The Nome King has turned Ev's queen and her ten children into ornaments in his palace. He lets each rescuer enter alone and touch objects while saying 'Ev,' and anyone who fails to find the royal family becomes an ornament too. Billina the hen overhears the King saying that Ev's people were made purple ornaments and Oz's people green ones, and this overheard rule lets the party restore everyone.
Princess Langwidere owns thirty interchangeable heads kept in a mirrored cabinet. She swaps them to suit her mood, and her temperament changes with whichever head she is wearing. When Dorothy refuses to trade her own head, Langwidere imprisons her, treating another person's self as an item to add to her collection.