Where 2NT asks opener to bid 3♣, which responder will pass or pull to 3♦, all with weak hands.
The thing is that you 'know' your partner has diamonds BUT if he had clubs you'd like to invite him and so you bid 3♦, which partner will pass with the suit or remove to 4♣ or 5♣, depending on his hand.
I've done this a lot, probably without the right hand and almost always have gotten an ill result.
Yesterday I held:
I was dealer and passed, and so did my LHO. My partner opened 2♥ (5♥'s and a minor), pass on my right and I bid...
3♦
All pass. Guess what dummy held...

Help

