If Pinocchio says 'my nose is growing now,' it must grow, and also absolutely cannot
Pinocchio's nose grows exactly when, and only when, he tells a lie. So what happens if, at a moment when his nose isn't actually growing, he says the sentence: 'My nose is growing right now'?
Reveal the answer
If the sentence is false, his nose should grow, which would make the sentence true. But if it's true, his nose shouldn't grow, which would make the sentence false, either way the nose behaves, it contradicts itself. Philosophers Veronique and Peter Eldridge-Smith formalized this as the Pinocchio Paradox in a 2010 paper, showing it's structurally identical to the ancient Liar Paradox, just wearing a children's story as a costume.
— Veronique Eldridge-Smith, Peter Eldridge-Smith, The Pinocchio Paradox — Analysis, 2010