In an online match, West led the heart king against four spades doubled and then switched to a trump. Declarer finessed to East’s king. So far, so good for the defense, but now East fell from grace by playing the club ace and another club. Declarer now had the entries to ruff away the defense’s diamonds via a finesse, making 10 tricks with five trumps, three diamonds, a club and a heart ruff.
East could have foreseen there was no rush to shift to clubs. If West had nothing in diamonds, he would have played a club at trick two, not a trump. An immediate trump return would have extracted a key entry from dummy prematurely.
There is more to this, though. When declarer plays a club from dummy at trick four, East must play the queen! Winning the ace instead would rectify the count for a minor-suit squeeze against West. When East ducks, declarer can win with the king, but that will not suffice.
South’s best bet now would be to lead another club, putting East back in the hot seat. That player must carry on the good work by shifting to a diamond. Declarer ruffs a club in order to ruff a heart, but she must then reach her hand to run spades and cannot do so without either trumping a club, destroying the menace in that suit, or ruffing a diamond and cutting the link with dummy.
It was precisely for this reason that the defense was dead once East cashed the club ace — a trump return is followed by the club king, a heart ruff, a club ruff and the rest of the spades for the minor-suit squeeze.