Margaret Whittingstall is a wastrel in Eel Pie Holm, she and others gather at night for duck soup. A rubber duck in a boiling soup pot. Arthur Hastings asks about this, she sees the duck as a sign of hope. Hope is the thing with feathers. Talfryn Fox says it's ridiculous and that it's used as a thermometer.
After the duck is thrown away, they believe that the duck was what caused all their problems.