For the source text click/tap here: Bava Kamma 56
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The mishna teaches: If the pen was breached at night, or bandits breached it, and sheep subsequently went out and caused damage, the owner of the sheep is exempt. Rabba says: And this first instance of a pen that was breached is referring specifically to a case where the animal tunneled under the wall of the pen and by doing so caused the wall to collapse. In that case, the owner is completely blameless and therefore exempt from liability for any damage that ensues.
The Gemara asks: But if the animal did not tunnel under the wall, what is the halakha? Would the owner be liable? What are the circumstances?
We explore the zoology and evolutionary advantage of tunneling in animals.