This pretty much covers it…

“The basic reality is that the risks that scare people and the risks that kill people are very different,” said Dr. Peter M. Sandman, a risk communication consultant in Princeton, N.J. “Risks that you control,” Dr. Sandman said, “are much less a source of outrage than risks that are out of your control. In the case of mad cow, it feels like it’s beyond my control. I can’t tell if my meat has prions in it or not. I can’t see it, I can’t smell it. Whereas dirt in my own kitchen is very much in my own control. I can clean my sponges. I can clean the floor.”

Dread is another factor, Dr. Sandman said. People can deal with sick stomachs, but they absolutely dread the idea of rotting brains. [NYTimes]