Immortal pressure, a pressure that could only be produced by an Immortal using his divine will.
Immortals were no longer mortals. After a cultivator transcended the Heaven Immortal Tribulation and became an Immortal, he would begin to learn the true colors and master the true power of the Heaven and Earth. Gradually, his Immortal Soul would begin to emanate a tiny bit of aura that contained the true principle of Heaven and Earth. When faced with this tiny and seemingly insignificant aura, any cultivator below the realm of Heaven Immortal would have to face an all-around spiritual pressure, as if a mouse was meeting a tiger.
Mortals could not sense any immortal pressure, as they were like the insects living in a filthy deep pond, who simply could not see what was beyond the pond.
