"Harry did not know what would happen if Ron touched the tentacles of thought now flying behind the brain, but he was sure it would not be anything good. He darted forwards but Ron had already caught the brain in his outstretched hands.... The moment they made contact with his skin, the tentacles began wrapping themselves around Ron's arms like ropes." (OP35)
This long, rectangular room is lit by lamps hanging low on golden chains from the ceiling. It is quite empty except for a few desks surrounding an enormous glass tank of deep green liquid. In this tank a number of pearly-white brains drift around. When removed from the potion in the tank, the brains fling out streamers of thoughts which can seriously injure someone if they wrap themselves around them. Other doors open off this room (OP34, OP35).