This is the scariest movie of all time. The author Gary Buslik, in A Rotten Person Travels the Caribbean, relates seeing this film at a resort in Mustique and heard a man behind him shout "Don't go in there! Don't open that door! Don't open that muthaf***in' door!". He turned to find that the man behind him shouting was Idi Amin. (1973)
The Exorcist