South plays in 3NT. Assume the S4 lead, won by the SA. East returns the S7 and West ducks, playing the S3. Dummy wins with the SQ.
Declarer can see that if he loses a trick with a failing heart or club finesse, he is likely to lose 3 more spade tricks for 1 down.
It is often right in this situation to give one opponent the opportunity to squeeze the other. So Declarer comes to hand with the DQ and leads a third spade. West cashed his three spade tricks and, with 7 cards remaining, exited with the C9, won by the CA.
Dummy's 7 cards were CAKJ6, D10 and H64. Declarer's 7 cards were C108, DAK, HAQ10. East probably kept CQ43, D5, HK95.
Now the play of the DA, DK, completes the squeeze on East.
If East keeps 3 hearts and the CQ, then Dummy's clubs are good. If East keeps 2 hearts and CQ4 then Declarer's hearts will be good, with a finesse of the HQ. (Note that West's discard on the third round of diamonds and West's discard on the second club help Declarer to get the play right.)