What kind of attack by a wild beast exempts the guardian from payment? The Mekhilta defines the standard: the attack must be by an animal that the guardian could not reasonably be expected to fight off. A wolf, a lion, a bear, a tiger, a leopard, or a snake — these represent forces so overwhelming that no guardian could be blamed for failing to protect the animal.
The principle derives from the Torah's use of "and it die" in (Exodus 22:9). Natural death is the paradigm case of unavoidable loss — no one can prevent it. The Mekhilta extends this to all situations where rescue was genuinely impossible. Just as the guardian is not liable for natural death, he is not liable for any attack where he was powerless to intervene.
This sets a high threshold. The list of predators is not random — it consists exclusively of animals that could kill both the entrusted beast and the guardian himself. A guardian might reasonably fight off a stray dog or a small fox. But facing a lion or bear? The Torah does not expect heroism. It expects reasonable care, and reasonable care does not include wrestling apex predators.
The conclusion — "for the torn beast he shall not pay" — applies specifically when the predator is of this caliber. Lesser threats, which a diligent guardian could have deterred, do not trigger the exemption. The standard is not merely "an animal attacked" but "an animal attacked that no reasonable person could have stopped."