"But,--sir,--I'm very sorry," said Gluck, hesitatingly; "but--really, sir,--you're--putting the fire out."
"It'll take longer to do the mutton, then," replied his visitor drily.
Gluck was very much puzzled by the behaviour of his guest; it was such a strange mixture of coolness and humility. He turned away at the string meditatively for another five minutes.
The above is from "The King of the Golden River" by John Ruskin.
I can't figure out what 'at a string mean'.