>>41020764 (OP)
They would be seeing the spiritual influx of light and spirits attracted to every object in the material world. They would be able to pick up objects and tell you about their memories and past.
They would have opened up multiple heavens inside them, and have a dual waking consciousness where part of them is exploring the spiritual planes, while still being able to function in the material world, although they would completely lose interest in the material world. They would be a vessel for God's light to flow into the world.
They would be able to read people's true character and karma just by looking at their aura.
If however they tried to blast open their third eye with dangerous techniques like drugs and/or possession, they would likely have opened up a portal to hell that would drive them insane with evil and deluded fantasies.