Continuity mistake: In the final hand, the first time we see Clancy's hand, it is the 8-9-10-Q of Diamonds; when the Kid calls, the cards are (a) reversed in order - Q-10-9-8) and worse, (b) throughout the entire movie, they are playing with Hoyle playing cards - but the reversed hand as well as Clancy's JD are from a deck of Bicycle cards, made by the United States Playing Card Co. In a real game, Clancy's hand would be dead, as it contains cards from an entirely different deck.
The Cincinnati Kid (1965)
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Directed by: Norman Jewison
Starring: Steve McQueen, Ann-Margret, Karl Malden, Edward G. Robinson, Tuesday Weld
Genres: Drama
Deliberate mistake: When The Kid visits the farm, the red truck in the background is a Fleetside truck that is definitely not from the 1930s.
Slade: How the hell did you know I didn't have the king or the ace?
Lancey Howard: I recollect a young man putting the same question to Eddie the Dude. "Son," Eddie told him, "all you paid was the looking price. Lessons are extra."