Spots

You're playing matchpoints, and you hold AQ KQ753 KT9 953. You reach 3NT opposite K86 842 AQ73 KT6. (Yes, your partner should have raised you, but he didn't.) The club 7 comes to the 6 and queen. What do you play?

You have 3 spade tricks, 3 or 4 diamond tricks, one or more heart tricks, but only after losing the lead, and a club trick if they return them. Your best chance is that the HA is onside, and that they can't run clubs. So you want to confuse the club situation, and should not play the 3. Now when the C4 is returned, the opening leader doesn't know whether their partner has Q4 or Q43. If it's Q4, then they need to take their A now, or they're never getting it. If it's Q43, then they need to duck a round to try to run the suit later. But if you've already played the 3 they know what to do and you won't get the crucial overtrick.

Now, let's look at it from my partner's perspective. She held J97 JT6 65 AJ872, and led a club to the 6, Q, and 5 and had the C4 returned and covered by the 9. She correctly ducked. If they find the falsecard, they win, but it makes more sense to play them to have been forced to play those cards. And in reality at the table I held Q43. After the club king held, I flew ace on the first heart play (necessary as it turns out if they guess well) and we ran the clubs.

The hand is also interesting from my side at trick one. You know from dummy and the rule of 11 that declarer has one card above 7. (You can see 3 of the 4.) If it's the ace, it's important to duck the 7 to prevent the finesse against partner's jack for three tricks. But otherwise you need to rise to prevent three club winners. Since Q caters to 3 of the 4, it's most likely to be right. And some partners would have led the 9 from J987 anyway.