Board 11

When North leads ♠A, it is essential for South to signal suit length. The normal system is high-low for an even count. Here, South should play the ♠8. North will interpret this as an even number, meaning that either the queen will fall under the king, or that South will be able to ruff the third round. North will continue with the ♠K. If South plays the ♠2 on the first trick, North will be reluctant to continue the suit, and declarer will make an overtrick by eventually discarding a spade on ♦Q.