Example #24 - Final showdown

3NT can be set on a H lead by South, but the remarkably convenient 1D opening puts an end to that.
Where East found a 3NT bid over 3D is anyone's guess, but like we stated before: missing cold games is bad practice.

Dealer E Vul All Scoring MP Lead ♣5	♠ QJ64 ♥ AT982 ♦ 93 ♣ 42
♠ AK32 ♥ Q53 ♦ K8764 ♣ J		♠ T9 ♥ K4 ♦ AJ52 ♣ KQ987
	♠ 875 ♥ J76 ♦ QT ♣ AT653

West	North	East	South
		1♦	p
1♠	p	1NT	p
3♦	p	3NT	p
p	p

You play CJ from dummy, North contributes the C5, you overtake with the CK and fire back C8 (!!) to the C3, S2, and C2.

You have 10 tricks for sure, but you might make 11 if you play carefully and opponents don't know the layout like you do.
When you cash 5 D tricks North holds on to S QJx and H AT9, while South has discarded a small S. Now you play a small H from dummy to your HK, cash S AK and play another S to North who is forced to let HQ make the last trick.

Of course, this was exactly the way Aruf played - but in the process something very revealing happened.
After winning C8, declarer continued with DJ!!!

Have a good look at the situation: there is no layout where the DJ play can gain, but there are plenty layouts where it simply costs.
The only possible conclusion is that declarer knew the layout and was showboating - he is literally shouting from the rooftops that he is using unauthorised information.