> is it desirable to use the fewest 'animal products'

Depends on what you mean. We "kill" billions of
"animals" on a daily basis by just breathing.

> is it possible for some people to be healthy
> vegetarians

I believe so.

> is it possible for all people to be healthy
> vegetarians

I believe not.

> what's the difference between a dog and a cow

Woof vs. moo?

Seriously, I think you mean "why do we  interact
differently with dogs than we do with cows". I've
wondered that myself. The Indian culture, after all,
reverses the relationship (cows being more "important"
than dogs). I think it's basically a cultural thing.
Hunters regard the dog as an ally because of its
hunting abilities. Herders regard the dog as an ally
because of it herding ability. Agriculturists regard
the dog as another food source.

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