What does 들 do?
It is the optional plural marker
When omitted, does it mean, "The cat is not food?"
When omitted it can mean "the cat is not food" or "cats are not food"
You would rely on context to determine if you are talking about a specific cat or the whole species.
I am able to do this. Cuz I watched a video where they explained the korean grammar in a sentence. PERSON + OBJECT +VERB.
what the different of 나는 and 제가?
Why do you have 이 after 고양 and then 은 after 들? Why do they bothe need a marker and why are is one subject and the other one topic?
In this case, 이 is not a subject marker, but part of the word 고양이, meaning cat. So you have topic + plural marker + topic marker: 고양이 + 들 + 은.
Sure about that?
How common are dog meat restaurants in Korea?
Rather common. Dog is sold as a stamina food.