The auction goes LHO : 1-of-a-Minor, RHO : 1♥ and now you come in with 2-of-the-other-Minor.
It is curious to see how difficult it is now for the opponents to explore a Spades fit (at least without incurring the risk of going overboard).
The following example (played on BBO yesterday) illustrates :
West opens 1♣, East responds 1♥. I (south) interfere with 2♦. West doubles and East bids 2♥ (taking the double for a support double). All pass.
Result 2♥-1. I would have been down 1 in 2♦. North - South can make 10 tricks with Spades as trumps.
You can blame it on the support double. But even if you decide to forgo such a valuable device doubling for Spades with a minimal opening is dangerous : if you find partner without 4 Spades you may be forcing him into making a bid that exceeds your safety level.
Basically, the 2♦ interference makes it very hard for the opponents to find a Spades fit unless :
- opener has reverse values (he bids 2♠) ; or
- responder has at least 11+ HCP 4♥4♠ (he doubles, accepting 2NT) or 12+H and 5♥4♠ (he reverses)
In other words, a 2♠ or 3♠ partial based on points divided, f.i., 13 - 9 (far more frequent than either partner having reverse values) is going to be really hard to get to.
And all that because of a tiny little 2♦ interference …
Remember : you promised not to use it against me.
(I first read this ‘secret’ many many years ago as an incidental remark about a deal in Mike Lawrence’s book “How to Play Card Combinations”. In the course of my readings I saw other authors mention it, do not know who was first to draw attention to it. I also do not know if the secret ever made it into some issue of the BOLS Tips series but, if not, it should have.)