Post Malone Hooked by Magic Trick While Performing in the UK

Post Malone was practically speechless after witnessing a scary version of Russian Roulette, involving a fish hook, 4 strings and a trick that grabbed PM ... hook, line and sinker.

The impromptu magic show went down Saturday night at the Reading Festival in the UK, where Post was performing. While hanging backstage with Tyla Yaweh, local illusionist Ryan Tricks gave the "Beerbongs & Bentleys" rapper a chance to inflict some serious pain.

Here's how the trick works -- Ryan puts a fishing hook into his mouth, which has four strings looped through it ... but only one of them is actually tied and firmly attached.

Now the queasy part ... Post was tasked with yanking on three strings (his manager, Dre London, ended up helping in the end) to see if he could pick the string that wasn't knotted.

You gotta watch this -- it's totally reminiscent of Christopher Walken and Robert DeNiro in 'Deer Hunter' -- except this is REAL LIFE. Honestly, we can't tell if this was a trick or just Ryan getting super lucky.

Post didn't seem too sure either, but he was more than happy to celebrate with the guy. Beers, of course ... what else???