There's a smell outside a lot of chain restaurants blowing out of the vents in the walls of the restaurant. I can't really describe the smell, it is a bit foody and savoury funnily enough. It kind of smells nice at first but then gets really quite sickening once you notice it. It can't be just the food because they all serve different food, is it something common to the way they prepare food, like those plastic bags or whatever?

What is that smell?