Was it Frankenstein? The Ring? Dawn of the Dead? The Blob? Godzilla? That episode of Trilogy of Terror with the doll? Some have voted Psycho or the Exorcist as two of the most frightening movies ever made. Alien is right up there near the top as its theme of infection and horrible death resonates with people.
But for my money most films are too transparent in their gore or attempts to shock to be truly frightening. Subtlety was often lost as film technology allowed creators to show in graphic detail what film-makers of the past could only hint at. While the immediate payoff and shock value rose the true fear, that of the unknown, waned. One over-looked “Master of Terror” who understood that horror usually requires some subtle direction is from Warner Bros. Studios and he worked exclusively in the animation department. That director is none other than Chuck Jones of Merrie Melodies and Looney Tunes fame.
Along with a crew of talented creators Chuck Jones helped produce for the movie theater market one of the scariest 7 minutes of film ever made, the animated short Claws For Alarm, featuring Sylvester the Cat and Porky Pig. Originally presented en masse to unsuspecting children during movie matinees in 1954 the film probably caused untold thousands in steam-cleaning bills to theater seats after each subsequent showing.
See for yourself at this link for those who can’t detect the embedded video: Claws for Alarm