The English actors were puzzled by Rod Steiger's method acting. Bernard Lee had particular problems with it but director Ken Annakin liked the animosity between the actors as it fit with the characterizations.
The dog was credited in the main titles as "Dolores", the name of the character. It was found in a dogs' home in Liverpool. Its trainer gained enough publicity from the film that he was able to set up the Dolores Dog Home.
This was one of Rod Steiger's favorite performances, though he was most proud of his work in The Pawnbroker (1964).
Although set in America, this was filmed entirely in England for the interiors and Spain (doubling for Mexico) for the exteriors.