East had been under pressure, and thrown two cards from each minor suit.
He would have succeeded if West had made the unlikely lead of a minor suit.
He expected to regain the lead in a minor suit.
East had to win with the jack and return a heart, squeezing West in the minor suits as he did so.
And if so, would West know which minor suit to lead?
This was natural, with 8-11 points and a possibility of a concealed long minor suit.
He needed two additional tricks from one of the minor suits.
East has shown at least 5-5 distribution in the minor suits.
South is sure to have length in one or both minor suits.
West had to guess which minor suit to attack, and guessed well.