There’s a saying in the mushroom-picking community that all mushrooms are edible but some mushrooms are only edible once.

That’s why, when news spread on Twitter of an app that used “revolutionary AI” to identify mushrooms with a single picture, mycologists and fungi-foragers were worried. They called it “potentially deadly,” and said that if people used it to try and identify edible mushrooms, they could end up very sick, or even dead.

Part of the problem, explains Colin Davidson, a mushroom forager with a PhD in microbiology, is that you can’t identify a mushroom just by looking at it. “The most common mushroom near me is something called the yellow stainer,” he told The Verge, “and it looks just like an edible horse mushroom from above and the side.” But if you eat a yellow stainer there’s a chance you’ll be violently ill or even hospitalized. “You need to pick it up and scratch it or smell it to actually tell what it is,” explains Davidson. “It will bruise bright yellow or it will smell carbolic.”

This is probably the most potentially deadly app I've ever seen pic.twitter.com/IrjuLSC6fZ — Grant Williamson (@ozjimbob) July 24, 2017

And this is only one example. There are plenty of edible mushrooms with toxic lookalikes, and when identifying them you need to study multiple angles to find features like gills and rings, while considering things like whether recent rainfall might have discolored the cap or not. Davidson adds that there are plenty of mushrooms that live up to their names, like the destroying angel or the death’s cap.

“but then your organs will start failing.”

“One eighth of a death cap can kill you,” he says. “But the worst part is, you’ll feel sick for a while, then you might feel better and get on with your day, but then your organs will start failing. It’s really horrible.”

The app in question was developed by Silicon Valley designer Nicholas Sheriff, who says it was only ever intended to be used as a rough guide to mushrooms. When The Verge reached out to Sheriff to ask him about the app’s safety and how it works, he said the app wasn’t built for “mushroom hunters, it was for moms in their backyard trying to ID mushrooms.” Sheriff added that he’s currently pivoting to turn the app into a platform for chefs to buy and sell truffles.

When we tried the iOS-only software this morning, we found that Sheriff had changed its preview picture on the App Store to say “identify truffles instantly with just a pic.” However, the name of the app remains “Mushroom — Instant Mushroom Plants Identification,” and the description contains the same claim that so worried Davidson and others: “Simply point your phone at any mushroom and snap a pic, our revolutionary AI will instantly identify mushrooms, flowers, and even birds.”

In our own tests, though, the app was unable to identify either common button or chestnut mushrooms, and crashed repeatedly. Motherboard also tried the app and found it couldn’t identify a shiitake mushroom. Sheriff says he is planning on adding more data to improve the app’s precision, and tells The Verge that his intention was never to try and replace experts, but supplement their expertise.

claims about “revolutionary AI” can be dangerous

And, of course, if you search the iOS or Android app stores, you’ll find plenty of mushroom identifying apps, most of which are catalogues of pictures and text. What’s different about this one, is that it claims to use machine vision and “revolutionary AI” to deliver its results — terms that seem specifically chosen to give people a false sense of confidence. If you’re selling an app to identify flowers, then this sort of language is merely disingenuous; when it’s mushrooms you’re spotting, it becomes potentially dangerous.

As Davidson says: “I’m absolutely enthralled by the idea of it. I would love to be able to go into a field and point my phone at a mushroom and find out what it is. But I would want quite a lot of convincing that it would be able to work.” So far, we’re not convinced.