The story "A Case Of Identity" also contains two subtle references to contract bridge, including a magic spell for establishing identity called the Jacoby transfer which requires blood from "at least two hearts." This is an allusion to a bridge convention known as transfer bidding, which attempts to make the stronger, concealed hand the declarer, and always results in a contract of at least Two Hearts. Also in the story, the murder victim is described as having been struck with a long club, because "according to the Kaplan–Sheinwold test, a short club cannot have been used." In the Kaplan–Sheinwold bidding system, making an opening bid of "one club" when holding two or fewer club cards-a "short club"-is not permitted.