The proper defense in today's deal is just meat-and-potatoes, but an East-West who aren't conscientious about signaling may let South get home.
South wins the first diamond with the king, leads a spade to dummy and returns the queen of clubs. When West takes the king, what should he do?
It looks easy for West to lead the jack of diamonds to set up his long suit, but what if South held 10 8 6, Q 10 5, A K, A 10 6 4 3? Then if West continues diamonds, South takes 10 tricks when a shift to a low heart would beat the contract.
Defensive "count" signals solve West's problem. When South leads a spade to dummy at Trick Two, East plays the three, showing an odd number of spades (five here). When dummy leads the queen of clubs next, East follows with the eight, showing an even number of clubs (four, presumably).
So West knows South has only three spade tricks, only three club tricks and two diamonds. Hence a heart shift isn't urgent; West can afford to continue diamonds.
You hold: 8 6 K 8 5 2 A K 4 A 10 6 3. With neither side vulnerable, the dealer, at your right, opens three spades. What do you say?
A: Pass. You'd happily double an opening bid of one spade. You'd also double a weak two-spade opening, though less happily. But your hand is too weak to double here and oblige your partner to respond at the level of four when he may be broke. Change your ten of clubs to the queen and you'd double.
A K Q 2
9 7 4
9 8 6
Q J 5
A J 6 3
J 10 7 3 2
10 9 5 4 3
8 7 4 2
K 8 5 2
A K 4
A 10 6 3
1 Pass1 Pass
1 NTPass3 NTAll Pass
Opening lead -- 3