Thus, the wizardly line about the octagons may be a metaphor - or perhaps they grow as the result of training. It also sometimes seems to be genetically inherited (although Disc heredity is complicated and self-distorting, or at least determined by personal background and very basic character traits. This sensitivity does seem to require a little training to be useful. Whatever it is called, the ability certainly enables the possessor to perceive all sorts of supernatural phenomena, including beings with Psychic Invisibility. Some even claim it’s just a matter of common sense and concentration. It is certainly true that magical adepts can see octarine, while other humans usually cannot, but witches, who work with subtler and less luminescent effects, rarely mention the subject they just know that they see things that other people don’t. They say that it is granted by the presence of octagons as well as rods and cones among the cells of the eye. Wizards often talk about this as the ability to see octarine. Magery, at any level grants the ability to perceive magical energies by sight. The Discworld RPG, developed in consultation with (and with the express approval of) Terry Pratchett contains this segment about ' Octarine vision'. I’ve always envisioned it as an orangey-purple, presumably because octarine sounds a bit like tangerine. This is referred to as ' octarine vision' and any mage (magic user) has it, regardless of gender. Witches can certainly perceive high magical fields.

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