If you are hooked onto a kind of lipstick, or any other kind of cosmetic, you will go back to that store again and again. And once you do, you're exposed to all the other things that the store carries.
Pet food is something that a lot of people need. Clearly, you are exposed to a lot of other things that are in the store. Let's put it this way: the lady might come into the store to buy pet food and might end up buying pet food and some lipstick.