McKenney Signals and Discards
West leads the ♦4 to the 8, Queen and Ace. Declarer plays Ace, King and another spade to West's ♠Queen. On the second round of spades, East must discard a diamond - the suit that is no use to the defence.
If a low diamond is played, then East is telling Partner that they want a club returned after the Queen of spades wins. If a high diamond is played, then East is telling Partner that they want a heart returned after the Queen of spades. If the ♦6 is played, then this is middle of the road, and doesn't say much about the required switch, i.e. Partner return what you think is sensible.
On this hand, East will discard the ♦9 on the second round of Trumps.
West will see this as a clear indication that East wants a heart switch. East will win 2 hearts (Queen and Ace), and eventually win a club trick. Note, if you are not playing McKenney, West might return the ♣10, which would be disastrous.
No club loser now.
West eads the ♥A, and sees the 10 from Partner, showing a probable doubleton, or possibly the Queen. West continues with the King, to the 3 from Partner. The continuation is now the ♥9 which East will ruff; the ♥9 is asking for the higher suit to be returned (we can discount Trumps - spades, so the choices are a diamond (high heart), or a club (low heart).
It is not obvious that East needs to return a diamond, and could equally return a club. This makes a difference of a trick.
However, East clearly sees that a diamond return is necessary. West wins the Ace of diamonds, and returns the 4th round of hearts, for a further ruff from Partner with the 8 of spades.
East will bid 2NT (Jacoby, showing at least a good raise to 3♥ or better); West can afford to splinter with 6 losers and a good hand. East has K Q of diamonds opposite a singleton - the worst possible holding, and therefore signs off.
North leads the ♠9 and South wins the Ace. South believes that the ♠9 might be a singleton, and would therefore like to give North two ruffs. If he shows a club interest (by returning the ♠2), Declarer might get it right, and finesse the Queen; better by far is a return of the ♠8 clearly asking for a diamond return. This way, the contract will be defeated by at least 1 trick.
South will bid 2NT (Jacoby, showing at least a good raise to 3♠ or better); North has got a good hand, but no Ace outside Trumps, and will therefore jump to 4S to show a good hand, but no 1st round control.
East leads the ♥2 and West wins the Ace. West knows that the ♥2 is either a singleton, or from 3 to the King, which would be a most unusual lead. It cannot be a doubleton, (high/low) or 3 small (MUD), nor can it be from a four card suit, since this would leave the opening No Trump bidder with a singleton heart - unlikely in the extreme. So, on that basis, West will try to give a Heart ruff. The size of the heart is again important, If West returns the 8 of hearts, this is showing the higher of the 2 suits outside hearts and trumps, i.e. diamonds; if the 4 of hearts is returned, then a club is required. It is important that East can have this information, otherwise there is no clear indication from dummy which of the minor suits should be returned.
West leads the ♦A; the first trick goes ♦6 from dummy, and ? from East, with South following with the ♦J.
The whole point about this situation is that there cannot be any benefit from West continuing diamonds! If South has a singleton Jack, then all that will happen is that a discard will be taken on the King of diamonds, and 10 tricks made.
So, it is far more meaningful for East to show where he would like West to switch to (the diamond that East will play will never show interest in the diamond suit. McKenney again.
If East wants West to switch to the lower suit, clubs, then the ♦3 should be played, as should happen on this hand.
However, if East wanted a spade switch, then the ♦10 should be played. So West plays the King of clubs at trick 2, a play that would be dangerous and impractical without McKenney, and continues with a club to the Jack (finesse), and finally the Ace of clubs to defeat the contract. Change East hand slightly, and give him
♠ K 6 4 ♥ 5 4 ♦10 6 4 3 ♣ K 8 6 3 and the play should be the ♦6. Decide for yourself Partner!!
North is somewhere between 2NT and 3NT, so temporises with a cue bid of the enemy suit. The final contract is reasonable. West obediently leads the ♠ 5, which hopefully looks like a singleton or doubleton to East.
East wins the Queen over the Jack, and hoping that West holds a doubleton, Plays the ♠A. West follows with the 3, as Declarer plays the 9. Trick 3 is what is called a trump promotion. Whatever Declarer does, West will now win the Jack of diamonds, in all likelihood. The spade that East returns is the 6. Again, this is non-committal. The 6 does not show any particular interest in any suit; therefore, when West wins the Jack of diamonds, the best return will probably be a heart - in the hope that Partner has the Queen.