“Ever so useful, string is,” the Doctor said brightly, tying a knot in the piece he’d wrapped around his finger. “I never go anywhere without a ball of string. You can tie things together with it, hang things up, even use it to keep from getting lost. It’ll hold your trousers up if you lose your belt, or replace a shoelace if you break one, and if you get bored you can tie knots in it.”
“So why’s that bit tied around your finger?” Amy asked him.
“To remind me to get another ball of string of course!” he replied.