Old Yeller

In 1860s post-U.S. Civil War Texas, Jim Coates (Fess Parker) leaves home to work on a cattle drive, leaving behind his wife Katie (Dorothy McGuire), older son Travis (Tommy Kirk) and younger son Arliss (Kevin Corcoran).
While Jim is away, Travis sets off to work in the cornfield, where he encounters "Old Yeller" (Spike), a Labrador Retriever/Mastiff mix. He was called that because "yeller" is an eye dialect pronunciation of yellow and the fact that his bark sounds more like a human yell. Travis unsuccessfully tries to drive the dog away, but Arliss likes him and defends him to Travis. However, the dog's habit of stealing meat from smokehouses and robbing hens' nests does not endear him to Travis.
Later, Arliss tries to capture a black bear cub by feeding it cornbread and grabbing it. Its angry mother hears her cub wailing and attacks, but Old Yeller appears and drives her off, earning the affection of the family. Travis grows to love and respect Old Yeller, who comes to have a profound effect on the boy's life.
Old Yeller's owner, Burn Sanderson (Chuck Connors), shows up looking for his dog, but comes to realize that they need him more than he does, and agrees to trade him to Arliss in exchange for a horny toad and a home-cooked meal. Sanderson takes Travis aside and warns him of the growing plague, hydrophobia (rabies).
One day, Travis sets out to trap feral hogs. On the advice of Bud Searcy (Jeff York), he sits in a tree, trying to rope them from above as Old Yeller keeps them from escaping. Travis falls into the group of hogs, one of which injures him. Old Yeller attacks it and rescues Travis, who escapes with a badly hurt leg. Old Yeller is seriously wounded as well. Searcy warns them of hydrophobia in the area and is chastised by Katie for trying to scare Travis. Fortunately, the boars did not have hydrophobia, and both Travis and Old Yeller fully recover.
However, the family soon realize that their cow, Rose, has not been allowing her calf to feed and may have rabies. Watching her stumble about, Travis confirms it and shoots her. While Katie and Lisbeth Searcy (Beverly Washburn) burn the body that night, a rabid wolf attacks. Old Yeller defends the family but is bitten in the struggle before Travis can shoot and kill the wolf. They pen Old Yeller in the corn crib for several weeks to watch him. Soon when Travis goes to feed him, he growls and snarls at him. After he nearly attacks Arliss, who, not understanding the danger, had attempted to open the corn crib, a grieving Travis is forced to shoot him. In doing so, he takes his first step toward adulthood.
Heartbroken from the death of his beloved dog, Travis refuses the offer of a new puppy fathered by Old Yeller. Jim comes home with a bagful of money and presents for his family. Having learned about Old Yeller's fate from Katie, he explains the facts about life and death to Travis. When they get back to the farm, the young puppy steals a piece of meat, a trick he learned from his father. Travis adopts him, naming him "Young Yeller" in honor of his father.

Question: What does Sanderson warn Travis about ?
Answer: Sanderson warns Travis about the growing plague hydrophobia.; Sanderson warns Travis about the growing plague hydrophobia.