Here's a hand from a matchpoints tourney I subbed in tonight.  It reminds me of how dangerous it can be to try to draw inferences against inexperienced players. 

Favorable in 1st

T2 / K5 / KQ9732 / QT7

 

I considered 1 Diamond, but it's a hair light.  I think it's the right bid, though, in retrospect.

I considered 2 Diamonds, but I didn't really want to miss game and I didn't want partner telling me he thought it was Flannery. 

Did I mention it was the last board of the tourney?

I bid 3 Diamonds.

LHO doubled (so far, so good.)  Partner passed.  RHO tanked for about 15 seconds and then decided we'd arrived.

Hmmm, maybe not so good.  At least with a slow pass I might have a chance.  Opps are 'Intermediates' (which also factored into my decision to open 3 Diamonds.)

LHO led the 2 of Clubs and I bought exceptionally well.

KJ43 / T9643 / T54 / 5

T2 / K5 / KQ9732 / QT7

RHO tanked for about 20 seconds and won the KING of Clubs (Huh?)  Then switched to the 8 of Diamonds (Huh?)

I was surprised RHO won the King of Clubs because either RHO has AK or LHO has made a very strange lead.  I was surprised RHO switched to the 8 of Diamonds because I expected her to have 4 Diamonds for her penalty pass, but surely at least 3.  What Diamond holding seems likely now?

Does RHO really have the AK of Clubs AND a Diamond stack?  That's not possible.  Am I supposed to play a low Diamond here?  If Diamonds are 2-2 with AJ offside, I'm gonna be sick.  Who would pass a takeout double with 2 small Diamonds?  I played the King.

LHO won the Ace and continued Diamonds.  Problem solved, but not the defense I was hoping for.  RHO contributed the Jack and I had this problem:

KJ43 / T9643 / T / -

T2 / K5 / 9732 / QT

How to continue from here?  Spade to the King?  Spade to the Jack?  Run the Ten of Spades?

Since the opps had killed one of my Club ruffs, I felt like I had to try to get a trick back.  While the Spade Ace is probably onside, if I play a Spade to the King, I'll end up losing 1 Spade, 2 Hearts, 1 Diamond and 2 Clubs for Down 2.  In this situation, -800 is death.  -300 and -500 are probably worth about the same (I think most of the time, with 26 High between them, the opps will play the hand in game and either make it or not, and -300 and -500 beat the folks who make it and lose to the folks who don't.)  -100 will beat the folks in a partscore their way.  I was hoping for +470 when dummy tracked, but I don't think that's in the cards any more.  I need to get to down 1.

I led the Ten of Spades, ducked smoothly.  Sigh.  I played low and RHO won the Queen.  Now the 8 of Hearts came back.  Wonderful.  Am I supposed to duck this?  What good will that do?  I played the King, losing as expected to the Ace.  Now LHO played the Club Ace.

Well, the good news is that my Club Queen is now good.  The bad news is that I'll never score a Spade trick now since my last entry to dummy has just evaporated.  Maybe someone will do something nutty (like duck) if I continue a top Spade.

Sure enough, something nutty happened.  LHO won the Ace and continued Spades, allowing me to pitch my 2nd Heart loser.  I escaped for -100. 

14 combined HCP.  Opponents cold for 4NT or 5 Clubs double dummy.  But I didn't expect this to matchpoint particularly well.  You've got to pick off the Club suit or go down in either game, and most folks won't manage it, particularly since the 3 Diamond (or 2 Diamond) bidder has the Club length.

Sure enough, -100 was worth only 40% of the matchpoints.

LHO

A765 / AJ2 / A6 / AJ82

RHO

Q98 / Q87 / J8 / K9643