The play suggests that East has four trumps. If so, his idea is to take the ace of trumps on the third round, at the point where you have only one trump left, and play a fourth heart. If this happens it will set up a second trump trick for the defense. The full deal:
There is only one way to frustrate this possible defense: discard a diamond from hand on the third heart and ruff in the dummy. When East holds up on the first two rounds of trumps, you abandon the trump suit and run the diamonds instead. However, as a safety play, cash a club winner first. This combination leaves East with no way to score a second trump trick. If he ruffs a diamond low, you will overruff in hand and continue to play minor-suit winners. If he declines to ruff, you will continue with the diamonds, throwing the three remaining clubs from your hand and make 10 tricks that way.
A trap is not cashing a club winner early. East can then discard three clubs and you will lose an embarrassing fourth trick.
