Virtually nothing is known of the Sentinelese language, and no word lists or language samples have been collected by researchers. It is presumably an Andamanese language, but how closely it may be related to other languages of that family is unknown.
They are actively hostile to unknown intruders requiring frequent shows of peaceful intent before allowing outsiders to come into arrow range. Attempts to leave them material goods from the late 1960s on have resulted in household ware and metal objects being utilized, coconuts being eaten but not planted (no local population of Cocos nucifera appeared to exist before the planting of saplings in 1987), pigs are not eaten but shot and buried, as was a doll. Red buckets were taken with apparent delight, while green ones were rejected.
A strategy that resulted in possibilities for close-quarter observation was that after an initial period of some 10 years, repeated dropping of material, chiefly coconuts, were deposited on deserted stretches of beach. Groups approaching to pick up the goods being monitored and censused from a safe distance, breaking off contact when the Sentinelese indicated they wished so by presenting their weapons and mock aiming at the contact party. Face-to-face contact was discontinued in the 1990s; more recent observations have been from a longer distance or from the air.