Describe IT

From the text:

IT was a brain. A disembodied brain. An oversized brain, just enough larger than normal to be completely revolting and terrifying. A living brain. A brain that pulsed and quivered, that seized and commanded. No wonder the brain was called IT. IT was the most horrible, the most repellent thing she had ever seen, far more nauseating than anything she had ever imagined with her conscious mind, or that had ever tormented her in her most terrible nightmares.