Castor's Folly and Pollock's Dream are supposed to be identical, but when shown together on the track after Grace dismounts Pollock's Dream, Castor's Folly is a golden color, while Pollock's Dream is a deep rich brown.
For the big race at the end, the horses first load into the gate on the turf course, however, all subsequent footage of the race is made up of a montage of multiple races on dirt.
When agent Rigsby holds the card deck against his forehead, he does so by holding it with one finger, initially. In the next shot, he is suddenly holding it with three fingers and instantly with one finger again after yet another camera switch.
Jane claims that covering all of the combinations in order to win him the trifecta cost him $5000. Yet a typical race has less than 13 horses 13 x 13 x 13 is 2197 possible combinations. He claims to have bet 50 cents but even at the normal $2 value of the smallest wager that's only $4394.