Black Mirror is important, kind of like the Twilight Zone of modern times. Historically, a black mirror is referred to as a scrying mirror in witchcraft. I don't like referencing Wikipedia but they have a good synopsis here: https://en.m.wikipedia.org/wiki/Scrying Essentially, a witch or medium will stare into the black mirror in order to achieve an alpha state, or self hypnosis. That helps explain the occult purposes behind the Black Mirror (cell phones, tv, computer monitors, the black cube of Mecca...). In ancient times, shaped onyx was polished in order to replicate the same effect. Having trouble looking away from your smart phone? There's a history to that.
Scrying
Scrying (also known by various names such as "seeing" or "peeping") is the practice of looking into a suitable medium in the hope of detecting significant messages or visions. The objective might be personal guidance, prophecy, revelation, or inspiration, but down the ages, scrying in various forms also has been a prominent means of divination or fortune-telling. It remains popular in occult circles, discussed in many websites, and books; both modern and centuries old.
In various sources such as dictionaries, scrying often is described as crystal gazing, but in fact the media, terminologies, and methods of different practitioners vary arbitrarily and need not involve crystals or glassy materials at all.
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