...when they are scared for their lives
http://www.webpronews.com/nightmares-fear-factory-has-the-best-flickr-photostream-ever-2011-10 *
http://www.flickr.com/photos/nightmaresfearfactory/
(easier "one click to see the next photo" here: http://www.flickr.com/photos/nightmaresfearfactory/6208606995/in/photostream/lightbox/ )
* a comment towards the bottom of that page tells you WHY there's such a consistent "scared for their lives" look on the faces of visitors