One of the delicacies Japanese cuisine is known for is fugu, a potentially deadly fish that people have been eating not only for centuries but for millennia. Fugu bones are found from time to time at Neolithic settlement sites as old as 4,000 years, suggesting that the history of it as food in Japan is quite long.

One such site is the Ubayama Shell Mound in Ichikawa, one of the many archaeological sites in the region. Dated to the mid-to-late Jōmon period (5,000-3,000 years ago), it has been excavated numerous times since 1893, providing a huge, diverse collection of shell and pottery specimens.

In 1926, archaeologists discovered the remains of a pit dwelling in Ubayama, in which a "family" of five—two adult females, two adult males, and a child—were found, striking the academic world with intrigue. The skeletons lay over one another and alongside them were fugu bones. Could this mean that they cooked the fish wrong and discovered its poison the hard way?

The answer is yet to be revealed, but recent DNA tests indicated that the child, a five-year-old boy, was not related to either of the women, contesting the conventional theory that one must have been his mother. The causes of their deaths are still unclear, but recent theories suggest that their bodies were laid on the floor by other villagers as a sort of makeshift burial, rather than them being victims of an accident, be it food poisoning or earthquake.

So far, a total of 39 pit dwellings and 143 human remains have been found at the Ubayama Shell Mound, making it one of the most notable archaeological sites in Japan. It was designated as a National Historic Site in 1967 and has been maintained as a public park, popular among kids and dog walkers unaware of the mysteries buried underneath.