West won with the king and returned a spade, a slight error.
But he did not immediately return a spade, which would have left East without a good play.
The queen went to the ace, and East returned a spade.
So West does best to return a spade for South to win with the jack.
Now he was down one, for East scored the heart jack and returned a spade to defeat the game.
West won with the queen and was about to return a spade when he paused to think.
East returned a spade to the king, and was now headed for trouble.
A better defense for East after taking the heart ace would have been to return a spade.
If he returns a spade, South will have no trouble.
But he could see breakers ahead if East won and returned a spade.