Why do people spit when they smell bad odor?

Answer 1

Odors effect sensitive membranes in your nose. Each odor has a unique effect on your nose and your body absorbs the essence of the odor through particulates caught in your nose. When you smell, for instance, a clogged toilet your nose is catching small particles floating in the air around the source. The body creates saliva and some mucous to flush out some of the particles, dulling the sense briefly and reducing the odor. It's sort of your nose's gag reflex.