A method of squeezing a player who does not guard a crucial suit, in order to drop a singleton honour, instead of taking a losing finesse.
Declarer, playing in no-trumps and needing the remainder, has a count of the hand and knows that West holds the ♠A in this example.
South leads the ♦A. West must discard a heart and dummy discards the ♠K. When South then leads a heart, he knows that if West has the ♥K it will show up because his last card must be the ♠A. When in fact West follows low, he will drop East’s singleton king.