Then east overtakes another club, cashes a third club, then, on the fourth club, promotes a trump trick in his hand. They have an eventual natural trump trick.
North can ruff but if so, west can get at least four trump tricks.
North must overruff with the queen, setting up another trick for the defense. East has an entry problem. North leads the spade jack, and west must ruff, south pitching a heart. East's hand cannot overtake the trump queen without promoting a trump trick in the south hand. Neither can east cash the club queen and get to his hand with a heart ruff, or south just pitches his high diamond and and a long trump.