France, Nov. 21 -- A tiny black dot moves across the sky over Bama, in north-eastern Nigeria. The roar of an engine grows louder, drowning out all other sounds in this town some 50 kilometres from Maiduguri, the capital of Borno State.

Kachalla, who is building a wooden door frame, pauses his hammering. "It's a helicopter," sighs the carpenter.

"In the Sambisa Forest, as soon as our leaders heard a helicopter flying overhead, they thought the army was watching them from the air. So it was every man for himself, we hid under the trees until the aircraft disappeared from view."

Kachalla looks up at the sky and watches the helicopter recede into the distance, then resumes his work.

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