A nice minor auction

N: ♠Axxx ♥KJ ♦AKx ♣Jxxx
S: ♠x ♥Qx ♦xxxxx ♣AKQxx

South opens 1♦. North responds 1♠
South bids 2♣. North bids 2♥, 4SF.
South bids 3♣. North bids 3♦, waiting, and below 3NT.

Now, South bids 3♥, a two-way bid. As a notrump probe, this suggests a lack of heart control. If South happened to have been slammish, then a notrump asking probe later proven to be a cue for slam purposes is a denial cue. (Had Opener bid, say, 4♣, instead, the BYPASS of a denial cue promises a heart control).

North decides to give up on 3NT and instead pursue a slam, which makes sense. So, he cues 3♠. This cue is sort of neat. Normally, a cue of a suit you bid would show two of the top three honors. However, in the context of a slam probe by a hand that has advertised 5-5 shape, that makes little sense. Rather, contextually this should show two things -- heart control (because of the denial aspect of the probe) and spade control, one of which is first-round.

South now bids 3NT, a non-serious 3NT call. With the minors, I prefer non-serious 3NT for the obvious reason -- partner can and often does want to pass.

North could pass now, which works out OK. But, suppose he bids on. IMO, the 3♦ call was ambiguous, as the last real call below 3NT that would be waiting. So, Responder should focus trumps. 4♣ by North, if he wants to move.

South now can now bypass 4♦ to deny good diamonds, bypass 4♥ (cheapest out-of-focus major would be RKCB), bypass 4♠ because he has nothing to contribute there, but bid 4NT as Last Train, because his clubs are so good. However, that call would make sense with the diamond Queen, not five small. Instead, he just bids 5♣.