Complex sentence: Dr. Tholan is researching a disease known as "Inhibition Death", unknown on Earth, and reveals his theory that a sixth parasitic non-physical intelligence exists that lives in the minds of the humans.
Split into simpler sentences: Dr. Tholan is researching a disease known as Inhibition Death, unknown on Earth. He describes his theory that a sixth, parasitic non-physical intelligence exists that lives in the minds of the humans.