The Mekhilta establishes a foundational ruling in the laws of property damage caused by animals. The question is straightforward: when is an animal's owner liable for the destruction it causes, and when does the animal's behavior fall outside the owner's responsibility?
The sages ruled that if an animal crossed a river, traversed a public thoroughfare, or scaled a fence ten cubits high (approximately fifteen feet) and then caused damage on the other side, the owner is not liable. The reasoning is that these barriers represent a reasonable standard of containment. An owner who kept his animal behind a river, a public road, or a tall fence has done what could reasonably be expected. When the animal breaches such a significant obstacle, the resulting damage is no longer attributable to the owner's negligence.
The Mekhilta then asks: how do we assess the range of an animal's potential damage in normal circumstances? The answer involves a specific measurement. The animal is envisioned as standing in the middle of a beth-kor — a large agricultural field measuring approximately 75,000 square cubits. From that central position, the animal's potential range of damage extends approximately 137 cubits in all directions.
Within that radius, the owner bears responsibility for any harm the animal causes. Beyond it — or beyond a river, road, or high fence — the animal has effectively escaped the owner's zone of control. This ruling balances two competing values: holding owners accountable for their animals while recognizing the practical limits of containment and the unpredictable nature of animal behavior.