Well, it's just the smell of cooking. My MIL has a thing about cooking smells needing to be kept in the kitchen. When we moved into this house, I expressed my interest in knocking out part of a wall to create a kind of bar area between the kitchen and dining area and she told me no way, because then your house always smells like whatever you've cooked. I was like...EXACTLY!! But she hates that and convinced my husband it was a bad idea, so he said no. I didn't push it because it wasn't hugely important to me and I was already having to battle with her about my bathtub and washer and dryer, and she doesn't even LIVE here...it's not her house, but she's very opinionated about how we decorate, etc. She tried to overrule me on the paint color, the wallpaper, the bathroom plans, the laundry room, the carpet, the curtains, the yard, etc... I gave in on the kitchen and held my ground on everything else. But she's very much of the opinion that kitchens should always be closed off to keep the smells from permeating the rest of the house. She also keeps her kitchen door open in the winter when she's cooking...it's always freezing, but she likes the ventilation to the outside.