Shock

Shock and Horror are different attributes to a Horror film, and create different effects within the picture.

Shock - Something that jars the mind or emotions as if with a violent unexpected blow.

In the film 'Un Chien Andalou' there is a scene where a woman's eye appears to be cut open. This creates a sense of unease for the audience, because the event is completely unexpected and shocking for them. When watching this, i personally felt shocked because of the fact that it appeared to happen to another human being, and is therefore something that could possibly happen to me.

A good way of creating shock is to create a sense of calm before the surprising event occurs. This lulls the audience into a false sense of security, and makes them feel safe. This is a common technique, used in nearly every horror film i researched. For example, the opening of '28 Weeks Later' includes a scene where one of 'the infected' appears suddenly, incredibly close to one of the characters. The character and the audience have very little expectation of the infected human being so close to the house, and it is used to create a shocking effect.

The clip can be found at http://www.youtube.com/watch?v=wHf6Th-E3kE, and the event occurs approximately 3 minutes through