Bidding: North, with 20 HCP, opens 1and is delighted to hear South respond1. North raises directly to game and South, with an absolutely minimum response, passes,since there can be no chance for a slam.
West leads the 2 in the hope that when he gets in with the trump Ace he will find a way to get to partner for a ruff. When the dummy comes down both declarer and East should realize that West's lead is a singleton -- it is not normal to lead the opponent's suit at trick one unless one is hoping to gain a ruff or give partner a ruff in the suit. The fact that the card is the 2 negates any possibility that the lead could have been from a doubleton. Declarer can win the lead in his hand or in dummy, and has no choice but to play trumps he is hoping to discard some losers on dummy's ’s later, but trumps have to be extracted first. West can see that it is very likely that his partner holds a black A (and hopefully the Q with it), but he does not know which one. How can he find out? The correct play when declarer leads trumps is to duck the first round in the hope that East has started with only one trump. If so, East will be able to signal on the second round of trump and this is in fact what happens. Then, East signals with the 8 as West wins his A. West duly shifts to a , East wins the A and Q and then gives West his ruff to set the contract. If West wins the first trump, he has to guess which suit to lead next; if he guesses wrong, South will make 5. Of course, if he guesses right, the contract can be beaten two tricks, as West will make both his small trumps on ruffs. But hoping to guess right is a poor substitute for a sure thing, since a lucky guess earns only an extra 50 points. At match points this may cost a little and the lucky gusser will get an undeserved top. But at IMPS this is fatal if you make the guess and it is wrong.