|♠||J 3 2|
|North to lead||♠||K 10 7|
A typical example is shown where spades are trumps and the lead is in dummy (North).
The ♥3 is led. If East ruffs low, then declarer overruffs low and cashes the ace and king of spades. If East ruffs high, declarer overruffs with the ♠K and finesses West for the ♠Q to make the remaining two tricks.
Devil's coups are fairly rare: not only the trump suit but the side suits must lie well for declarer.