RESEARCH - What is Shock?

http://www.dictionary.com/ defines shock as 'a sudden and voilent blow or impact; collision.'

Shock is very hard to define, but it is in many horror's and I want the audience to feel it in my film.

The below clip is an extract from the surrealist film; by Salvador Dali, 'Un Chien Andlou'. The film was banned for many year's due to its unacceptable and shocking footage. That extract left me feeling shocked, I believe this was due to the randomness of the act, and the goriness of it. I would like to achieve this feeling in my film, as a horror is meant to leave their audience shocked, terrified and horrified.