The toxicity of a substance is dependent on the "route" by which it enters the body. Routes into the body might be ingestion by mouth, via the lungs, inhaling substances as vapours or aerosols, absorbing substances through the skin, and snorting things up the nose to be absorbed by the fine blood vessels in the nasal cavity, etc. The latter accounts for the vastly increased absorption of cocaine, for instance, when it is snorted, rather than eaten. That is, the activity or toxicity of the compound is greater by the nasal route than by the alimentary route. In the movie Pulp Fiction, one character almost kills herself because she snorts heroin, thinking it is cocaine. Maybe this is because it has greater "route dependent toxicity" when it arrives in the body via the nasal route - the blood vessels in the nasal passage deliver drugs directly to the cerebral cortex - rather than the usual intravenous route preferred by heroin addicts.