Ben-Hur - Mixed Up Horses
In the scene where Judah is hugging his horses just before the chariot race, he calls the one with the gray mouth "Aldebaran" and scolds "Rigel" for biting him. However, in the earlier scene where the Sheik introduces the horses to Judah, Rigel is the horse with the gray mouth (like all the others, Aldebaran has a white blaze on his mouth). Since Judah knows and loves these horses well, he wouldn't mix them up like that.
1959 version of Ben-Hur