Sheeana feels a kind of gravity assert its rules on the void and allows herself to drift in towards the well.

Accelerating faster, she hits the corrupted ground with a sensation like all the blood in your body pulsing into your head for two hundred and seventy eight milliseconds.

A Fremen's ecological instincts and a Bene Gesserit's enhanced senses help her sense out the corruption. It stank, clawing at her nostrils with black and oily fingers. Even though she could not feel Other Memory here, she knew what it would say. A Harkonnen scent. Even now, five thousand years later, there is an oily feel to Gammu's sand.

And there she saw the 'worm' too, the one from the Outsiders' 'pool'.