2NT was a game-forcing raise, 3D showed a singleton, 4C and 4H were cuebids, 4NT was a keycard ask, and 5H showed two keycards without the queen of spades.
E-W let the momentum of the auction push them into slam, even though neither partner had extra values. They couldn't escape two heart losers, and 6S went down one.
East was now gun-shy. Even though everything was cuebid, he didn't have anything extra for his bid, so didn't think he should push on any more. They languished in 4S making 6.
How can we help poor E-W with these two hands? Maybe West should cuebid 4H on the second board, but not cuing a king-empty fourth certainly isn't a sin.
A simple solution has been devised for these situations: "Serious 3NT".
Serious 3NT is a convention that's only on when the partnership is forced to game and have agreed on a major. When those two criteria are met. a 3NT bid by either partner says "I have undisclosed extra values, and am interested in slam," and a cuebid that bypasses 3NT says "I don't have any extras, but I'm cuebidding just in case you have slam interest."
Playing Serious 3NT, the first auction should go like this:
1S - 2NT; 3D - 4C [I have a club cuebid, but no extra values]; 4S.
Once responder is known to not have extras, opener knows they don't belong in slam, and signs off. A cuebid of 4H over 4C would show slam interest even though he knows his partner doesn't have extras.
With Serious 3NT, the second auction could go like this:
1S - 2NT; 3D - 3H; 3NT [I have lots of slam interest!] - 5S [I'm chock full of controls, the only thing I'm worried about is the unbid suit, clubs]; 6C [I have clubs pretty well wrapped up] - 6S.
Some players [including myself] have started playing Non-Serious 3NT. This is basically backward from the original Serious 3NT - bidding 3NT denies extra values and cuebidding above 3NT shows extras and slam interest.
Back to the first auction, with Non-Serious 3NT:
1S - 2N; 3D - 3NT [I don't have any extras, but I want to leave room for you if you do]; 4S [I'm not too loaded either. Let's stop here].
The second auction:
1S - 2N; 3D - 3H; 4C [I have slam interest and clubs controlled] - 4D; 4S [I've done my all with the diamond shortness, club cuebid, and showing extras] - 4NT [my controls plus your extras has to be a good thing]; 5H [two without the queen] - 6S.
Why play Non-Serious rather than Serious 3NT? I think it works better because it doesn't give away information to the defense when you're going to stop in four of your major anyway. When neither partner has extra values, keeping the defense in the dark can be very helpful.