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Lets say you find yourself in the airport in Kuala Lumpur. A stranger approaches with a spray bottle and a fistful of money and points to a man who looks more than a bit like the half-brother of North Korean dictator Kim Jong-Un. Must be a coincidence, you think.

The stranger explains that shed like you to star in a hilarious prank TV show that asks ordinary citizens to spray random people with water for the lulz. Whats the risk, right? Right?

Wrong. Congratulations. You just got punkd into becoming an international assassin. It was strangers on a train in a terminal.

In all seriousness, if its true that Siti Aisyah, the woman suspected of killing Kim Jong-nam by spraying him in the face with an unknown substance, didnt know what she was doing, could she have known better? How would anyone have known better?

Science is how. But in the world of chemistry, distinguishing water from weapon can be a lot trickier than youd think.

So what do you do, really? The first tool available to the responsible prankster or citizen scientist is eyeballs. Give that spray bottle a close look. Is it a clear or translucent one, or is it opaque and heavy-duty? Plenty of potentially harmful chemicals have to be shielded from light to avoid photochemical reactions. Corrosive materialslike fluoroantimonic acid need to be stored in something even tougher, like Teflon.

But a clear bottle containing clear liquid doesnt mean youre, well, in the clear. Some really nasty substances, like sulfuric acid (which probably wouldnt kill someone even at high concentrations, really, if you just spritzed a persons face with it) and cyanide solutions, look pretty watery. Some chemicals are more viscous or syrupy than water, says Gabriele Ludewig, a toxicologist at the University of Iowa. Theoretically, with something like sulfuric acid, which has a higher viscosity than water, youd be able to swirl your pranking bottle and see adhesion forces drawing the liquid together into rivulets and dropletslike those wine legs your oenophile friend wont shut up about. If your chemical is in a dilute solution, though, youre pretty much out of luck.

Eyes failing you, you might turn to your nose. Dont! Many harmful chemicals are odorless, especially in solution, and the risk is just too great. Its not good to smell these things, says Nien-hui Ge, an analytical chemist at the University of California Irvine. It could harm your respiratory tract badly. Plus, the vapors of some chemicals, like nitric acid, can blind you. So thats out.

Dont taste it, although this was once a thing. Fifty, 100 years ago, chemists would describe substances by color, smell, and taste, Ludewig says. But nowadays were a little more careful. And no one knows what most of this stuff tastes like, anyway. Everybody knows a polonium solution is toxic, so no chemist with a sense of self-preservation is going to lick it for the sake of science. That should go double if youre suspicious of the mysterious prank show producer in front of you. I would never want to taste it myself, Ge says. Even if you get just a little bit of something like cyanide dissolved in water, it will kill you.

Absorption through the more callused hand is very inefficient compared to mucus membranes. Gabriele Ludewig, University of Iowa toxicologist

Well, prankster-assassin, youre out of applicable senses. Time to head to the lab. An environmental toxicologistwho, not even kidding, didnt want to be named for fear of causing an international incidentoffered this advice: The first thing I would do is treat it like its definitely not water, and get it under a hood (the chemistry kind of hood, a box that contains potentially harmful vapornot the car kind or the Mark Zuckerberg kind).

From there, the tools of scientific world are your potential poison-identifying oyster. A litmus test will show you whether its acidic, basic, or neutral (hint: water should be a neutral pH 7). A good place to start. And then you go for the good old gas chromatography-mass spectrometry, and its sloshier cousin, liquid chromatography-mass spectrometry. Those analytical methods break substances into their constituent molecules and identify them, so thatll often tell you what youre dealing with beyond reasonable doubt.

Theres even a portable version,so youve got no excuse not to add it to your packing list next time your flights connect through Kuala Lumpur.

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How to Avoid Getting Tricked into Assassinating Someone - WIRED