puzzle box

noun4

1. •
   A box that cannot be opened by the usual obvious means, and therefore challenges a person to find the correct way to open it.

   • "Jest like the Injian puzzle-boxes, ain't they?" said Dan, as the one boat dropped into the other. — 1896
2. •
   A similar device or cage that can be opened by means of levers, latches, etc., used to test the learning behaviour of animals.

   • That’s where Osvath’s ravens come in. His student Can Kabadayi trained the birds to open a baited puzzle box by putting a stone of particular weight and shape into a tube. — 2017
3. •
   (figurative) Something that is puzzling; an enigma; (narratology, also attributive) a complex story that is gradually revealed, often driven by a central myth.

   • But Memento is one of his finest efforts, a brilliant film that reveals new layers on every rewatch thanks to its puzzle-box plot structure. — 2021
4. •
   A box containing a jigsaw puzzle.