North led 8 against 3NT, to the 3, 9, and K. Presumably because he expected diamonds to be 7-1, declarer led a club to dummy's jack. Then he cashed dummy's top hearts, pitching a spade while North threw a diamond, and the ace of clubs, then came off dummy with a spade. South split his honours and declarer won with the ace.
Now he had a decision to make. If clubs were 3-3, he should cash the king of clubs, but on the actual lie he should endplay North with a diamond exit. How can he tell?
Diamonds are almost certain to be 6-2, or South would not have split his spade honours. So North is 2263 or 1264. But which? Experienced opponents won't have been helpful with the club count, but there are two clues: first, even third in at green North might not have opened 3 with the balanced hand. Second, at matchpoints, North would probably have pitched a spade if he had two, rather than a diamond, not wanting to lose an undertrick if South had the ace of spades.