http://www.theory-test.co.uk/asp/hpt_flashdisplay.asp
Perfect example video, an experienced driver would click a few times at the beginning but all the dsa is bothered about is the idiot in the beetle pulling out and how soon you recognise it as a "developing" hazard.
i.e do you click when you see the guys walking to the car as you think they may pull out or wait till the car moves.