After the king of spades lead it was natural to overtake to play a club in case partner has the ace of clubs. That would have been 4 tricks but maybe partner has some sort of trump trick, who knows.
In practice my club return ran to the king in dummy and after pulling trump, declarer took out my ace of diamonds, and it was +1 (partner unblocked the queen of spades - not the point of discussion).
After the board my screenmate started laughing and pointed to the ace of clubs under the table that I had dropped some time between the auction ended and when dummy was put down.
Bottom line I think I play autopilot on defence a little too often.

Help

1♠-2♥-2♠-x
p-3♥-all pass