In the years since India won independence from the British, groups of anthropologists have tried to study them.
But no one has managed to get through. Several times, Mr. Pandit said, the Sentinelese have turned their backs on anthropologists and squatted down, as if they were defecating.
In 2006, two Indian fishermen who accidentally washed up on their shores were killed. When a military chopper flew low over the island, some men fired arrows at it. These days, the Indian authorities aren’t taking any chances. The Navy enforces a 3-mile buffer zone around North Sentinel. But police suspect Mr. Chau went at night with the intention of circumventing the authorities.
It is unknown what the Sentinelese call each other, or whether any other group in the world understands their language. When an expedition brought members of another indigenous tribe to North Sentinel, thinking they might share linguistic similarities, neither side understood one another.