Not the most credible theory, but it reminds me of the "Hedgehog in the cage" mechanical puzzle: https://en.wikipedia.org/wiki/Hedgehog_in_the_Cage https://en.

Not the most credible theory, but it reminds me of the "Hedgehog in the cage" mechanical puzzle: https://en.wikipedia.org/wiki/Hedgehog_in_the_Cage https://en.wikipedia.org/wiki/Hedgehog_in_the_Cage So maybe there's a wooden/metal piece that goes inside, and the challenge is to get it out?