Breast or Bottle?

I was on an errand when I ran into an old Duroux family friend who stopped to congratulate me. He asked me a strange question though, which I've been thinking about ever since: "Est-ce que tu nourris ton enfant?" It's silly when taken at face value -- of course I nourish my child -- but what he was really asking was if I did it au sein or au biberon. Kind of a personal question to field from someone that isn't within your intimate circle of friends... I suppose the important thing is that my child is bien and not mal nourri (3 kilos!).

*au sein breast-feed; au biberon bottle-feed