Clue: 'The REM Introduction' begins with eerie instrument (8)
Answer: THEREMIN
Explanation: Definition: eerie instrument
Just what it says on the label: '**THE REM IN**troduction begins with'. The is an early electronic instrument, notable for being played without physical contact: the player's hands are waved in the vicinity of two antennae, controlling pitch and volume. Its speciality is eerie glissandi, as in this clip from Hitchcock's (scored by Miklós Rózsa).