Yes, many of you guessed correctly, the dagger is a fishbone! To be precise, it’s a bone from the head of the Ya fish (雅鱼, a type of carp also known as 丙穴鱼), which is a speciality of the western Sichuanese town of Ya’an. (you can see a picture of the fish here). The fish, which is often made into a claypot stew, is famously tender, with few bones and delicious savoury flesh.
On the left, you can see a Ya fish, presented dramatically in a cloud of dry ice in its raw state, to be cooked in the dining room, in the pot on the left-hand side of the photograph.
My hosts that night mentioned some colourful legends about the knife in the fish’s head, and I’ve done a little research today. There seem to be a few different versions of the story. Some say that the bone was formed when the creator goddess Nu Wa 女娲，while patching up holes in the sky, let her double-edged sword fall into the waters of the river at Ya’an, far below. One tells of an evil river demon who demanded that a beautiful girl be given to him as a bride, threatening calamitous floods if the people of Ya’an failed to oblige him. A young woman volunteered to save her community by offering herself up as his wife, and she challenged the demon with a double-edged sword. All the fish in the river, so the legend goes, decided to commemorate the bravery of her sacrifice, by forming an image of the sword in their heads, and using it to suppress the river fiend.