The Laughter

Lethal version: Contact with Joker venom causes uncontrollable spasms of laughter, followed by a painful death. Some have speculated that the venom hyper stimulates the laughter functions of the brain, leaving the victim unable to breathe, cutting off oxygen from the brain. It is also possible that this drug contains the tetanus toxoid responsible for lock jaw. Patients often exhibit a grotesque grinning expression called "Risus Sardonicus" due to spasms of the facial muscles.

Non-lethal version: The venom causes uncontrollable laughter and momentary loss of cognitive function, but instead of dying their faces are pulled into an unusually large grin for the duration of it's affects. Prolonged exposure to the non-fatal variant will cause permanent brain damage.