Follow the play here, and ring the metaphorical bell when you think the defense has slipped against my three-no-trump contract.
West led a fourth-highest heart three to East’s king, and back came the heart 10 to the jack and queen. West cashed the heart ace next, but sadly East’s nine and seven blocked the way. East had to win the fourth round of hearts, and West’s long card withered on the vine. Nine tricks made.
It is easy to see that West made the final mistake by cashing the heart ace. He could have unblocked the suit by continuing with a low one to East and overtaking on the way back. However, the original fault lay squarely with East. How was West to know that I, declarer, did not hold three hearts? Then it would look silly to underlead on the third round when the whole suit was cashing trivially as long as West played it from the top.
In fact, the key error was that East played back the wrong card at trick two. Pinning dummy’s heart eight could not be critical, so East’s return ought to be the seven, giving current count. Thus, when West wins with the heart queen, he knows that East has an odd number of cards remaining, because the seven is smaller than both missing spot cards. While it is easier at pairs than teams, maybe West ought to steel himself to underlead his remaining heart honor at trick three, on the grounds that declarer either has two hearts left — a surefire trick — or zero. The heart 10 is the card East would return from an original K-10-x.