This was a teen, not an adult, but still:
My brother had some friends over. My mom made veal parmesan. One of the girls didn't know what that was:
Mom: Veal? You know?
Girl: *blank stare*
Mom: Veal is baby cow. You know, like lamb is baby sheep?
Girl: People eat sheep?
I was almost going to say in this thread that I wonder how anyone with two brain cells cannot understand where food comes, even without being told it. I never remember being told, it was so clear, we would eat chicken and pig and so on, and you know they are animals too. But then I started to wonder the English language, and how there is beef and pork and so on. I'm not a native speaker, but I've understood that these terms are usually used about meat, not really as "oh, there is the pork walking around, saying oink". So maybe it's not as clear if your mother says it's going to be pork today compared to if she would say it's going to be pig today.
As I understand it, this difference in words for the animal and the product that comes from it comes from a linguistic divide in English history when the ruling class and the working/farmer class spoke two different languages.
So the working class Anglo-Saxon farmers would call the animals by the name of the animal (because that what they saw mostly, the whole animal) like Cow, Sheep, Pig.
The ruling class Norman elite who never really saw the full animal, only the final processed product used words like Beef, Mutton and Pork.http://www.straightdope.com/columns/read/2008/why-do-we-eat-beef-and-pork-rather-than-cow-and-pig
This could be a historical fairytale, but it's still a nice explanation of the split.
I have been known to jokingly say "We're having oink sausages today", or answering a question about what kind of burger I'm eating with "Cow", but that's just me being silly and nonsensical. Using the name of the animal just sounds wrong. "Pig sausages" just sounds kind of gross, no matter how accurate it may be.