Joker Venom is the Joker's signature weapon and a chemical compound for various purposes including killing, paralyzing or stunning victims.
Contact with Joker Venom causes uncontrollable spasms of laughter followed by a painful death. Some have speculated that the venom hyperstimulates the laughter functions of the brain, leaving the victim unable to breathe. It is also possible that this drug contains the tetnus toxoid responsible for lock jaw. Victims often exhibit a grotesque grinning expression called "Risus Sardonicus" due to spasms of facial muscles.
The venom causes uncontrollable laughter, but instead of dying, their faces are usually pulled into an unusually large grin. Artists often stylize the effects; adding yellow teeth, bulging eyes, paleness, etc. similar to Joker's features himself. Prolonged exposure to the non-fatal forms can cause permanent brain damage.