This deal from an EBU duplicate demonstrates a useful piece of defensive technique.
West led a heart against four spades. Declarer won in dummy and played a spade. East won with the ace and played back the eight of hearts to give suit preference for diamonds when West ruffed the heart.
How do the defenders ensure that they get all their heart ruffs?
West should return the queen of diamonds, East wins with the ace and plays back the seven of hearts to indicate possession of the diamond jack as an entry.
West can now underlead the diamond queen to get East in to play a fourth heart to allow West to get all his heart ruffs.
Similarly if West had started with KQJx of diamonds and East had A10xxx West can start with the jack of diamonds and East can show the ten of diamonds by playing a high heart.