Talfyrn Fox is a wastrel in Eel Pie Holm, he and others gather at night for duck soup. A rubber duck in a boiling soup pot. Arthur Hastings asks about this, Talfyrn explains it's used as a thermometer to see when the soup is hot enough. Richard Kerr complains it's a decoy.
After the duck is thrown away, they all believe the duck was to blame for their fighting.