I see The Laundry has been restocking their Hand of Glory reserves.
Is it bad that I'm pleased that I get the reference?
Haven't seen any concrete seagulls though.
The bird nerds at the local wildlife rescue here call that "string foot". Bird, usually pigeons, get a foot tangled in some discarded string-like garbage and slice it off.
Life in the big city!
I suspect rather than actually slicing it off, the string (probably often monofilament, at least near fishing areas) cuts off the circulation, and the tissue dies.