Ever wondered how to use your phone to produce a holographic image of a dolphin inside a glass dish? Me neither, but now I've seen it happen in a viral TikTok that's doing the rounds, I'm ready to call it one of the best optical illusions I've seen online. The video, which has currently amassed nearly 4M views, features Tiktokker reddnea 'projecting' a holographic image direct from her iPhone. And apart from the Tupperware, it's all very Blade Runner. All you have to do is place a transparent sheet of plastic inside the dish, then play a 3D holographic video (there are tons on YouTube ). The result is what looks like a floating object inside the dish. But you might be surprised to learn that this is an optical illusion that long predates the smartphone. Known as Pepper's Ghost , the trick has been used in theatre and cinema for decades, with English scientist John Henry Pepper first popularising the effect during a theatre show in 1892 (thanks, Wikipedia).…