One day I found myself sitting against Mark Lair (who was playing with a client), and this entertaining deal came up:

IMP-15		North		Dlr: South
Board 510		-
		A75
Client		KQJ94		Lair
J4		KQJT2		AK976532
JT963				2
A876		Me		-
94		QT8		8765
		KQ84
		T532
		A3

Me Pass Dbl Pass All Pass

West Pass Pass Pass

North 1(?) 4NT(?) 5

Lair 4 Dbl Dbl

Lair led the K, which my partner ruffed. The contract is cold if North just draws trumps and knocks out the A. The defense can take at most one spade and one diamond, since dummy's spade holding acts as a stopper. But declarer proceeded to draw three rounds of trumps, pitching the T from dummy. He continued with a diamond to the ten and ace, Lair pitching his heart. With the client on lead, Armageddon loomed:

		North
		-
		A75
Client		KQJ9		Lair
J		T		A976532
JT963				-
86		Me		-
-		Q		8
		KQ84
		532
		-

You can see now what happens if West returns a spade. If North ruffs, Lair ruffs the next trick and runs all his spades for down 5! If North refuses to ruff, Lair of course overtakes the J and continues spades to knock out North's last club. But West returned...a diamond! Lair ruffed, but that was the end of the defense. Making 5 doubled, 550, was only worth 4.97 IMPs because some people were making 6. It will be a while before I see another declarer and defender give and take five (doubled!) tricks to each other on one board. ("Here, you take them." "No, no, I insist they're yours." "I can't accept, you take them....")