Explanation:

Distinguishing Characteristics:
- A dog, horse, and cat are domestic animals commonly kept as pets, while a fox is a wild animal.
- Dogs, horses, and cats are all mammals, while a fox is also a mammal but belongs to a different family called Canidae.

Habitat and Behavior:
- Dogs, horses, and cats have been domesticated for centuries and have adapted to live among humans, while foxes are primarily wild animals that prefer to live in forests and other natural habitats.
- Dogs, horses, and cats have specific behaviors and characteristics that make them suitable for domestication, while foxes have different behaviors that are more suited to a wild environment.

Physical Characteristics:
- Dogs, horses, and cats have distinct physical features that make them easily recognizable, while foxes have a different appearance with characteristics such as a bushy tail and pointed ears.
- Dogs, horses, and cats have been selectively bred by humans for specific traits, while foxes have not undergone the same level of domestication and breeding.
In conclusion, the odd one out from the given options is the fox because it is a wild animal with different characteristics, behaviors, and habitats compared to dogs, horses, and cats which are commonly domesticated animals.