Posted 2013-March-31, 21:51
Mbodell gives fine auctions, but when I was a beginner I wouldn't have been able to parse this: "3 spades is initially thought by N as a probe for 3nt but is revealed as a slam cue for hearts with the pull to 4hearts, keycard and 6."
So, basically what it means is that after 3♥, if the sides don't have a fit (N doesn't know that they do), it makes sense for them to try and play 3NT on sheer power. So, 3♠ shows a stopper in spades (or shows in clubs and asks for spades, matter of agreement). N, assuming they're in a misfit and holding the desired club stopper, bids 3NT. Now S suddenly bids 4♥. Since S is the one who asked for NT with his spade bid, pulling to hearts is a surprise. In this case, showing heart support (two cards at most, since with three he'd have supported hearts instead of bidding 3♦). Since he didn't raise 3♥ to 4♥ directly, he is probably trying for slam, with a spade control.
I hope I didn't explain the obvious.