Looking up I realised it was the sheath of the flowers of a palm that, after hanging for about a year, had dried out, curled up to form a heavy headed spear, and dropped vertically. The point is very sharp, so in future I'll give the thing a wide berth. It's too high now to take off the sheaths -- my ladder only takes me four metres.
Would have been a quick end - unless it had merely penetrated my shoulder... better not think about that... like the time I embedded an axe in my shin bone... doesn't do to think too much about such things.
