Judging from the opening lead that East holds the ♦A, South plays the ♦9 from dummy at the first trick, ruffs in hand, and draws trumps.
Hoping that West holds the ♥A, South leads the ♥7, executing Morton's Fork: Note that declarer must be careful not to play a high diamond on the opening lead, as East could then withhold the ace.
South must get a discard on a diamond honor eventually, but not before West has been forced to decide whether to take the ♥A or duck it.
NW ES Robert Gray[3] gives this spectacular example of an impossible defense to Morton's Fork.
South wins and leads a heart, covered and ruffed.
Gray points out that to defeat the contract, West must lead the ♥2 at trick one.