Question:
halacha states that fish and meat is dangerous and one can get tzara’as.
how should this danger be explained to a non frum Jew?
Answer:
You can simply tell him that the Talmud says that it is dangerous, therefore we don’t do it. Although this danger is not recognized by modern medicine, and it may be possible that the nature of people has changed, nevertheless since the Talmud says it, we adhere to it.
