Fear
Rui thoroughly used Plurichroma to understand how the catoblepas communicated different colors and sounds. He thoroughly covered all bases, taking his time with the various shades of each color.
He went even beyond the normal human range of visible light and audible sound, getting even more data and only stopping when the catoblepas could no longer sense the light and sound.
He was finally done.
He immediately returned to communicating the image of the Divine Doctor in his mind, embodying it once more as he deployed it through subconscious non-verbal communication.
Instantly, the non-verbal communication of the catoblepas shifted.
"MOOOEEEAAAUUU!"
They began thrashing and struggling in a futile attempt to run away, growing increasingly emotionally distressed.