Smilex gas

In the 1989 movie, when Bruce Wayne reads through the police file on Jack Napier, he learns that Napier, despite his criminal ways, is extremely intelligent and especially gifted in art and chemistry.

Joker venom is the means by which Joker terrorizes Gotham City when he first appears in his new guise, slipping components of the toxin into household products such as cosmetics and cleaning fluids, in such a way that when used together, the products become deadly. In a mock TV commercial, he refers to the "special ingredient" as "Smilex" and later attempts to wipe out hundreds of Gothamites with Smilex gas via giant festival balloons.