You find a box in the attic.
In this box are aerosol cans labeled “Bugspray”. At the bottom of the can, nestled in the concave niche, is a dial. The dial has labels for gnat (the dot on the dial is here), dust mite, fruit fly, housefly, black widow, radioactive tarantula, AIDS-III-carrying mosquito, and giant man-eating cockroach.
Pressing down the nozzle releases an angry cloud of gnats, as indicated on the dial. A warning label on the can states that the can should not be exposed to open flames.