As you can see, 5! offered no play, even though it was likely to escape being doubled, but, if he had been allowed to play there, would South have made 4!?
Presumably, West leads a club and declarer wins, draws trumps and ruffs dummy's remaining club in hand. Then he leads a low diamond, which West must duck, and the king wins. The next diamond lead draws the queen from East, and West must overtake and cash his jack. Now, with the other suits eliminated, West must lead a spade or concede a ruff and discard, after which a winning spade guess by declarer will see him home.
West, of course, must not lead the 4A, but the 44 does the trick as long as East contributes his nine. Then, having to play the remaining 4K,5 facing 4J,7,3 himself, declarer must lose two tricks in the suit.Reuse content