2,349. Believing the Butcher
Maachalos Assuros 8:6
If someone eats the sciatic nerve from a neveila, a treifa or an animal that was sanctified as a burnt offering, he is liable to two sets of lashes. Since these prohibitions include the rest of the animal’s body, which was previously permitted, it also includes the sciatic nerve. This causes a second prohibition to be added on top of it.
Maachalos Assuros 8:7
When removing the sciatic nerve, one must dig out all traces of it until there’s nothing left; a butcher’s word is accepted regarding the sciatic nerve, the same as it is regarding forbidden fats. We therefore don’t buy meat from just any butcher, only from those who are considered upstanding and who have good religious reputations. If the butcher both slaughters the animal and sells the meat, his word is accepted.