 Eno used a piano as a <unk> instrument and mixed the result with the drum loop through a <unk> effects unit to create a sound that bassist Adam Clayton called " eerie and foreign and scary " . Lanois stated that the processing of Mullen 's beat , which resulted in a drone @-@ like sound , became the song 's backbone and personality . Clayton described it as " evocative of that sinister death squad darkness " . Colm O <unk> of Hot Press felt it was " the key sonic element " because it " [ evokes ] an abstract sense of evil and <unk> " . 
