On the other hand in 1867 the merchant ship Nineveh reported that the Sentinelese were armed with iron tipped arrows so they can't have been that isolated. Clearly they were getting metal from somewhere.
Even recent reports from this century and a few decades prior have confirmed the islanders have some iron arrowheads.
They get their metal by scavenging shipwrecks. Given the Andamans are on a well-traveled route, this could have been going on for a while.
Exactly what I thought when I first learned they have at least some iron arrowheads.
They could have also made them from the few iron pots they've gained over the last two centuries. Once the pots puncture or are otherwise damaged and unusable, maybe at least one was taken apart gradually, cut up into metal shards and the shards sharpened into arrowheads. Though metals washed up on the shore or in the form of shipwrecks made a lot of sense too, and would be a more common source of metallic materials.
interested if they have metal where do they get it? can't imagine that island would have a source, what sort of wildlife food sources are there besides fish? snakes, lizards?
I'm not sure snakes would live on that fairly small, fairly isolated island. Perhaps
sea snakes that swam there, but they wouldn't be seen much outside of the coastal areas. Depends on whether the Andamans have any snake species, really. If not, I think it wouldn't be surprising if North Sentinel Island also lacked snakes. From what I know about island evolution, lizards tend to arrive later than plants, insects, turtles (or seals) and birds. And snakes even later. When humans discovered New Zealand, it had no snakes whatsoever, and that's effectivelly a mini-continent. (Compare Ireland in Europe, which also doesn't have a natural snake population of its own, though that's down to the ice age rather than oceanic isolation.) Snakes are generally late animal colonisers, if they make it at all (colder climates being naturally more prohibitive to this).