Why is a small chest important for a Jack Russell Terrier?

A small chest is particularly important for a Jack Russell Terrier because it allows the dog to maneuver into tight spaces, especially when hunting or burrowing. These dogs were originally bred for hunting foxes and other small game, requiring them to fit into narrow burrows to flush out their prey. The compact structure enables the Jack Russell Terrier to navigate these environments effectively.

This specialized physical trait is closely tied to the breed's working history, as their ability to enter tight holes is vital in their role as hunting companions. This design feature aids not just in the action of going into a burrow but also allows them to be agile and quick in confined spaces, making them exceptional hunters.