Interesting

A K 8 5 4 3
A 4
Q 10 9
9 8
J 10 6 2
Q J 9 8 7 5 6
6 3 J 8 7 5 2
A Q J 4 7 6 5 3
Q 9 7
K 10 3 2
A K 4 Contract: 6 spades, 6 no
K 10 2 Opening lead: Q of hearts

Six spades in one case by way of a no trump opener by South and a transfer bid by North. Two declarers made their slam here on the same opening lead. One did it through astute playing, the other through a totally bizarre defensive misplay.
I'll start with the latter: declarer won the opening lead with the A in dummy, took three rounds of trump, ending in the closed hand, led the 10 of hearts, which held. Which held! West held the J 9 8 of hearts at that time (he'd thrown 2 hearts on trump leads), and he couldn't cover that 10? Well, not just cover, but win the trick? Against a slam contract where he also holds an ace? Declarer now cashed the K of hearts, sluffing a club, whereupon he could claim, conceding a club trick. It's all the more bizarre in that hoping to hold a tenace position over the 10 is the basic logic of leading a Q from Q J 9. Who has escaped leading the Q on such a holding and been dismayed to see A 10 5 when dummy comes down. I dunno.
The other declarer ran six spades and three diamonds, which comes to 10 tricks, counting the heart opening lead. If declarer had trouble discarding, well, so did West. They each held three cards, declarer holding a stiff K of clubs and K 10 of hearts, West a stiff A of clubs and J 9 of hearts. The 10th trick was a diamond toward the Q, on which the Q of clubs came sailing out (the J had been discarded earlier). Declarer reasoned well. He hadn't seen any 9 of hearts come sailing out. So at trick 11, he laid down his K of clubs, and West, winning with his ace had to lead from his heart tenace into declarer's. Well done.
Could West have avoided that situation? No, it wouldn't seem so. Had he kept two clubs and a singleton heart, declarer could drop the heart and cash the 10. Note the value of the 10 on that hand. You can't tell aforehand and they're not part of the hcp count, but 10's can often be a key card for declarer or for the defense.
And if West had led a diamond or spade on opening lead? I confess that at first thought, West could then beat the contract. But no, West would be squeezed before rectification of the count on 9 leads (6 spades and three diamonds). He must keep three hearts and two clubs, which of course you cannot do after 9 tricks. If he doesn't keep three hearts, declarer can drop the Q J, and if he does, he gets down to a stiff A of clubs, and declarer can then play the suit exactly as he did.