Music, Sound effects

Music 

For me a film needs music, as well as the setting the makeup and the lighting,music is one of the key parts. It helps to add tension as well as make the movie appear more fluent. The music can help set the scene and help to add to the horror. 

Some people could say it allows the film to stop looking realistic however when you watch a film you never realise it is there, but somehow it helps to make the viewer jump without you realising it was the music.

Why does the music scare us?
Film makers have long relied on disturbing pieces of music and soundtracks to help heighten suspense and terror.  Scientists say that the harsh discordant and unexpected sounds in horrors imitate the screams and frightened animals. They followed out a study. The study concluded that the use of these non-linear sounds was not random - but used to 'enhance the emotional impact of scenes'. 'Non-linearities are commonly produced when animals are under duress, such as the fear screams produced when animals are attacked by predators,' he said.

Noise of panic 

The simplest examples of this are found in thriller and horror films, which employ dissonant, screeching sounds we unconsciously associate with animals in distress.
In films like Hitchcock's 1960 classic Psycho, straining strings and overblowing brass are mimicking the noise of panic in nature. Some filmmakers are now using infrasound to induce fear in audiences. These extreme bass waves or vibrations have a frequency below the range of the human ear.

   

A film without music 

However some films tend not to use music when trying to build tension as sometimes it can distract you from the horror and make it less shocking.