So I have a funny story involving this phrase. When I was in Sweden for the first time meeting my husband's parents (boyfriend at the time), he told me that if I did not understand what they said to me, that I should just respond with "Jag vet inte". As it turns out, I was not feeling well one of the days I was there and his mom asks me if I was pregnant. I was not pregnant, but me not knowing any Swedish at the time, responded to her with no other than "Jag vet inte". My husband had some explaining to do to his mother after that. LOL!