Warning: spoilers for Batman/Catwoman #5!
The Joker has utilized plenty of deadly weapons and tricks throughout his lengthy comic book career, but the most memorable and disturbing of all is without a doubt his laughing gas formula (also known as Joker Venom). Now, within the pages of Tom King and Clay Mann's recently released Batman/Catwoman #5, the Joker's method for testing the effectiveness of his laughing gas has been revealed, and it adds a whole new level of depravity to the already horrifying weapon.
The Joker's laughing gas has been around since the earliest years of the Batman villain's history. Though its effects and means of dispersion have varied throughout the decades, its core function has remained largely the same: once it enters a victim's bloodstream, the toxin causes instantaneous and uncontrollable outbursts of laughter, followed shortly by death and a large Joker-like smile stretched across the victim's face. It's a cruel but ever so fitting tool for the Joker who's known for imparting his belief that life is nothing but a meaningless joke in the end, even if he has to do it by force.
Batman/Catwoman #5 picks up on Selina Kyle/Catwoman and Andrea Beaumont/the Phantasm's confrontation from the previous issue. Andrea, a former lover of Bruce, has returned to Gotham to extract vengeance on the Joker for killing her son. Though Andrea knows it would be a fool's errand to try and convince Batman to hand the Joker over to her, Selina on the other hand doesn't exactly share the same unwavering moral principles as the Bat. So, Andrea sets out to persuade Selina that she should be allowed to kill the Joker by revealing the Clown Prince's secret method for perfecting his laughing gas formula.
Andrea introduces Selina to Sal Neismann, a Joker fanatic turned loyal henchman who she captured and chained up. She explains to Selina that Sal was tasked with gathering fellow Joker devotees and conning them into following him back to the Joker's hideout to be used as living test subjects for the laughing gas. It turns out that throughout all the years of the Joker implementing his deadly toxin among innocent civilians, there were entire groups of people manipulated off-panel into being mere guinea pigs for the horrible weapon. Selina is understandably disturbed by this revelation and chooses not to stop Andrea as she kills Sal right in front of her.
So much of what makes the Dark Knight a compelling and admirable hero is his stringent no-kill rule, no matter the circumstances. Yet some of the best Batman stories push the boundaries and reveal to readers the gruesome nuances that go undetected in the average Bat-story, challenging them to consider just how righteous the Caped Crusader really is to allow an irredeemable psychopath like the Joker to go on living. Selina's loyalty, much like the reader's, is put to the ultimate test by the point Andrea conveys to her about the Batman's code - that realistically, a whole lot less people would be dead if he were willing to sacrifice just one. As unpleasant as it is to learn of yet another horrific detail behind the Joker's signature laughing gas, it makes one wonder what other appalling truths lie on the outskirts of the Batman's nightly Gotham escapades.