Philip Dormer Stanhope, 4th Earl of Chesterfield, who died in 1773, wrote to his son, "Prepare yourself for the world, as the athletes used to do for their exercise; oil your mind and your manners, to give them the necessary suppleness and flexibility; strength alone will not do."
In this column two days ago, East played the heart jack from Q-J-4, third hand high. Yesterday, he played the queen from the same holding under his partner's ace-lead, to show the jack. Today, East needs flexibility of mind. Defending against five diamonds, West leads the heart two. After declarer calls for the king from the board, which heart should East play? Why?
South's jump-rebid of three diamonds showed a good six-card (or longer) suit and 15-17 high-card points. (Some players would rebid two no-trump.) North's leap to five diamonds would not meet with universal approval.
East would normally play the heart queen at trick one to show his sequence. But here East should assume that his partner has led a singleton. (With a doubleton, West would have led his higher card. And with 6-3-2, West would surely have picked another suit -- or led the six, top of nothing.) If West does have a singleton, he would like to know where East has an entry so that West can receive a heart ruff. East should give a suit-preference signal, dropping the heart six, his lowest card to indicate that his entry lies in clubs, the lower-ranking of the other side suits.
West grabs the first trump trick, shifts to the club nine, and receives the critical heart ruff.