Assuming that trumps break, eleven tricks are clearly available in the form of six diamonds, the club Ace, and two Ace-Kings. The 12th is available via the club hook or the heart Queen coming down tripleton. If that happens, then the club finesse or many other squeezes might make 13 tricks. If declarer takes the club finesse, he can get a 13th trick by either ruffing a club in dummy or via a squeeze, the most likely of which is a double squeeze around spades, though heart-club or spade-club simple squeezes are possible. What is the best line?
Clubs 3-3 with the King onside is a trifle under 18%. The heart queen dropping is almost exactly the same---just a bit under 18%, but is inferior to clubs because the hand is not over yet even if he finds the heart Queen. The squeezes are a little harder to compute. If clubs are 3-3 (35.53%) then East and West need to have sole guard over one of the majors and declarer must guess the position. If East has four clubs to the King, however, then if he has five spades (unlikely on the lead) or five hearts or four hearts with the Queen, he can be squeezed. That comes to about 10%. If East has four clubs (including the King) and West has the heart guard, then a double squeeze around spades arises. That is about 8%. Is it possible to combine chances somehow? Perhaps. The opponents are looking bored, and it is unlikely to cost to cash two heart tricks right away.
On the second heart, East drops the ten without much thought. This looks like a true card; how does that affect the odds? Greatly. This means that the heart Queen is very likely to drop; if not, hearts are guarded in the West, so the double squeeze is competitive. It must be best to ruff a heart and run the trumps. Either a real squeeze or a defensive error is likely to occur. On the third heart, the Queen does appear and the slam is home when trumps break in a civilized fashion.
As the cards lay, this was the only winning line, and the reward for getting it right was a trip to Copenhagen.