This hand looks to be a quiet part score but careless defence let declarer make too many overtricks. The auction was as shown. As West, I would prefer rebidding 2S for the same reasons as one would transfer to 2S over a 1NT opening. South had to find a lead and, with two unbid suits, it is clear to lead one of them. Often, it is correct to prefer an unbid major but East might have rebid 2C holding both minors. The fact that they didn’t makes a club more attractive. Also, East might have a heart suit but not enough values to be able to bid it and that makes the heart less attractive. There is also less rush to try to set up a suit defending 1NT than there is defending 3NT. For these reasons, and the safety of the solid sequence, South led the QC. North overtook with the AC and returned the 9C which looks like an initial three card club suit. South knows that something has gone wrong because this would mean East has 5 clubs and that is inconsistent with the auction. Teams, None vul, Dealer South
♠On winning the 10C, South tried the heart suit to no great avail and declarer ended with 10 tricks. North explained that the club play was an attempt to unblock the clubs. Let us examine this closely. The lead of a queen against a no trump contract promises QJ10 or QJ9 at the head of the suit. Since North has the 9C, South is known to have QJ10. If the defensive clubs are 4- 4, there is no possible blockage. If South has 5 clubs, then East has precisely king doubleton and the king will appear on the second round. The potentially blocking 9 will be put under the JC or 10C without any stress. Thus, the only case where North needs to be wary is the case in point where South has the short suit and North has the fourth round winner. North needs to make the standard return of a low club showing an initial holding of 2 or 4 cards and this removes the danger of accidentally promoting the 8C to being a winner.