For the source text click/tap here: Bava Kamma 21
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If a dog or a goat jumped from a rooftop and broke vessels while doing so, their owners must pay the full cost of the damage. Thus saith the Mishnah and an exact Braitah.
This indicates that if they fell off the roof, they would be exempt from all liability despite his obligation to keep them from climbing onto the roof and jumping down from there.
The Gemora infers from the Mishna that the reason for liability is because the dog or goat jumped from the roof but were it to have fallen down from the roof (and then broke utensils), the owner would be exempt. It can thus be inferred that the Tanna of our Mishna accepts the view that when a situation begins with a negligence (for the owner was not guarding his animal on the roof) and results in a mere accident, the owner is not liable to pay.
We explore the curious history of punishing animals in the medieval period for crime committed against humans.