Commentary for Avodah Zarah 68:12

Resh Lakish here distinguishes between two situations. If one slaughters an animal in order to use its blood or fat for idolatry, the very act of slaughtering does not yet render the animal prohibited. Only inside the Temple would his intention to perform an ancillary act for idolatrous purposes effect the status of the animal. But if he slaughters the animal itself for idolatry, then the animal is prohibited. It was to this case that Resh Lakish referred when explaining the prohibition of Bithynian cheese.