Kim Jong Nam, the half-brother of North Korean dictator Kim Jong Un, died in a Malaysian airport on February 13 after two women rubbed a poison on his face. It’s unclear why Nam was killed, and who was behind the plot. But this story gets more mysterious, more dramatic, and weirder by the day.

On Friday, Malaysian authorities reported that the poison that killed Nam was VX, a chemical “weapon of mass destruction” that the United Nations banned in 1993. This is no drugstore poison: VX is one of the most toxic chemical substances ever to be manufactured.

Here are five things you should know about it.

1) VX is a nerve agent, and is a nasty way to die. Nerve agents kill by interrupting the communication between nerve cells. Specifically, it inhibits the process that breaks down the neurotransmitter acetylcholine, which is responsible for muscle contractions. “If acetylcholine does not break down,” New Scientist explains, “muscles stay helplessly contracted, and victims die of paralyzed breathing.”

And that’s not all. VX causes convulsions, and victims will often foam at the mouth.

2) VX is an oily liquid that’s both odorless and tasteless, and has the consistency of honey. It can be aerosolized and sprayed as a nerve gas. Reports indicate that Nam was killed by VX in liquid form.

3) VX was banned worldwide in a 1993 United Nations treaty.

The British scientists who first synthesized VX in 1955 wanted to kill insects. But they quickly realized they’d created something so powerful it could kill people too. The British government took notice, studied VX for its potential as a chemical weapon, and eventually shared the recipe with the United States. In 1993, the UN banned VX at the Chemical Weapons Convention, a treaty forbidding the stockpiling and use of any chemical weapon of mass destruction. The US destroyed its remaining VX stockpile in 2012, the New York Times reports.

4) VX is absurdly potent, and a little bit can go a long way. By bringing it into a crowded airport, the assailants put many people at risk. According to the National Academies of Sciences, a lethal dose can be as low as 0.04 milligrams per kilogram of bodyweight. For a 150-pound person, that means just 2.72 milligrams — just a speck — placed on exposed skin can summon the reaper. Ten milligrams, really just a drop, is thought to be a lethal dose for most people. “VX is at least 100 times more toxic than sarin,” which is another potent neurological poison, the National Academies reports.

5) VX can be created on the spot by mixing two chemicals. The Guardian reports this is likely what occurred in the airport:

Raymond Zilinskas, who directs the chemical and biological nonproliferation programme at the Middlebury Institute of International Studies in California, said it seemed unlikely the killers applied VX directly. “Even if they were wearing gloves, the fumes would have killed them,” he said. He suggested the assassins might have used a “binary concoction”, smearing two non-fatal elements of VX which mixed on the victim’s face.

We still have a lot of questions: Did the women create the chemical through this process? Or did they simply walk into the airport with fully lethal VX? Did they have an antidote on hand? Was the VX imported from North Korea? And, most of all, why resort to VX?

Whoever is the perpetrator here, they wanted to show the world they have this weapon and are willing to use it.