Now East has only losing options:

-          He can take his ♣A and persist with Diamonds, in which case Dummy ruffs (with the Ace!), trumps are drawn, and the ♣Q is an entry to Dummy’s Hearts.

-          He can take the ♣A and return a Club (knocking out Dummy’s entry), in which case Declarer can scamper home on a cross-ruff, scoring one Heart, one Club, and all eight of those trumps.

-          He can duck the ♣A, in which case it’s another cross-ruff.

 

That was delicately timed, as drawing even a single round of trumps early in the play would be a mistake.  Look what happens: Diamond opening lead is ruffed, Spade to Declarer’s King, ♥A, Heart to West’s King, Diamond ruff, ♥Q ruffed by West, ♣J covered by the King and Ace, Club to Dummy’s Queen.  Now Declarer has an awkward guess … if the remaining two enemy trumps are split then Dummy’s Ace must be cashed before running the Hearts … but if East has both missing trumps (the actual case) then the Hearts must be played first.  It’s better to avoid that guess!