The dish that the two men ordered was albatross. They had been stranded many years earlier on a desert island. When the man tasted albatross he realized that he had never tasted it before. This meant that the meat he had been given on the island was not albatross as he had been told. He correctly deduced that he had eaten the flesh of his son who had died when they first reached the island.

This has something in common with No. 9 above but is in my opinion even better. It is fiendishly difficult to figure out from a standing start. A beautiful aspect of this problem is the subtle fact that he shot himself because he did not recognize the taste of the dish!