Tim McCanlies wrote the lion as a female, because he thought it would be easier to keep under control than a male lion. It wasn't until production began that he found out that female lions were actually much more ferocious than male lions.
In the fight scene with Robert Duvall against the four teens, one of the actors, Travis Willingham, was hit three times in the face by Duvall. Due to a miscommunication, Duvall reportedly told him afterward, he thought that Willingham was a stunt man and that he, Duvall, was supposed to hit him. The cut used was the final one when Travis' nose finally started to bleed.
EASTER EGG: On the special features side of the DVD, go to the deleted scenes section. While at the top of the list, press the "up" button on your remote control and a star will appear and be highlighted. Press the "Okay" button and a clip of outtakes will come on showing all of the filmmakers' attempts at trying to put the rooster on the pig.
Although Jasmine the Lion is frequently said to be old and weary, Taureg, who played Jasmine, was a young lioness, less than two years old (lions in captivity can live up to 20-22 years). This is stated in the DVD special features.
Michael Cain has said that early in his career he once held Sean Connery's hat while he fought and beat four men in a nightclub single-handedly. This may be the inspiration for the scene in which Robert Duvall's character also fights and defeats four men single handedly while Cain and Osment watch.
The lion in the movie is a mixture of reality and puppetry. Like in one scene where Hub, Garth, & Walter were looking at it, they weren't really looking at the lion. From inside the crate, they were looking at the puppet lion moving the head like it was actually moving.
Haley Joel Osment was contracted without knowing which studio would make the movie and who were the other main leads. This was against standard Hollywood practice and surprised Eugene Osment (Haley's father and manager) at first, but he agreed to "use" his son to get the remainder of the cast and the studio.
When Walter was wrestling with Jasmine, a female stunt double named Marie played Walter with her hair cut really short when shooting the scenes with the real lion. When Haley Joel Osment plays Walter, you can see behind the head that it is the puppet lion.
The shoulder patch on the uniform of the Sheriff who meets with adult Walter shows Copeland, Texas, (not Comal County, Texas). This helps account for the missing letters (not enough room for Comal County, which does not display on sheriff patches) and the fact that corn does not do well in South Texas black clay in Comal County, but does do much better in North Texas red clay near Smith County (where Copeland is).
Secondhand Lions is the second time Robert Duvall and Kyra Sedgwick have played relatives in a movie. In Secondhand Lions they were uncle and niece. In "Something To Talk About", they were father and daughter.