Terry is a personal friend.
Denis has known Terry for 25 years, working with him during the first 8 years. My personal version of the story, as told by Terry one lazy evening over a meal and a few beers, differs slightly from that of the book. As the otters rely heavily on their sense of smell and not recognising the scent of the jumper, bit the end of Terry's left middle finger not realising that it was him. As Terry tried to pull the otter off with his right hand, the otter turned and bit the end off the tip of the middle finger on his right hand. As they were on staying an remote island off the Isle of Skye, it was days before Terry was able to leave to get medical attention, hence gangreen had set in.