It was Jackstraw who heard it first - it was always Jackstraw, whose hearing was an even match for his phenomenal eyesight, who heard things first. Tired of having my exposed hands alternately frozen, I had dropped my book, zipped my sleeping-bag up to the chin and was drowsily watching him carving figurines from a length of inferior narwhal tusk when his hands suddenly fell still and he sat quite motionless. Then, unhurriedly as always, he dropped the piece of bone into the coffee-pan that simmered gently by the side of our oil-burner stove - curio collectors paid fancy prices for what they imagined to be the dark ivory of fossilised elephant tusks - rose and put his ear to the ventilation shaft, his eyes remote in the unseeing gaze of a man lost in listening. A couple of seconds were enough.
'Aeroplane,' he announced casually.