There is a trick. The "How is this possible?" primes the LLM that there is some kind of trick, as that phrase wouldn't exist in the training data outside of riddles and trick questions.

The trick in the original question is that it's a twist on the original riddle where the doctor is actually the boys mother. This is a fairly common riddle and I'm sure the LLM has been trained on it.

Yes there is. The trick is that the more common variant of this riddle says that a boy and his father are in the car accident. That variant of the riddle certainly comes up a lot in the training data, which is directly analogous to the Schrödinger case from above where smuggling in the word "dead" is analogous to swapping father to mother in the car accident riddle.

I think many here are not aware that the car accident riddle is well known with the father dying where the real solution is indeed that the doctor is the mother.