The content of Sabbaths songs (both originals and cover versions) from the two first albums demonstrated a tongue in cheek interest in the occult and black magic. This was a crucial step in establishing the 'darkness' and 'heaviness' of later heavy metal lyrics, and Black Sabbath was the first group to feature such lyrical content, almost to the exclusion of other topics. Led Zeppelin, The Doors and others might have hinted at magic or the occult, but few contemporaries could match Black Sabbath for directness, such as "My name is Lucifer/Please take my hand" (from Black Sabbaths "N.I.B."). Butler wrote most of the lyrics.
Another innovation was the by-product of an accident: Iommi's fretting fingers were injured in an industrial accident slightly before his early tenure with Earth. He was working in a sheet metal factory at the time and the tops of the two middle fingers on his right hand were sliced off. Initially, he forged himself prosthetics from a melted plastic detergent bottle. The injured fingers were understandably tender, so Iommi downtuned his Gibson guitar from standard E to C#. The resultant slackness of the string allowed him to play with less bother to his fingertips. Butler also downtuned his bass guitar to more easily follow Iommi's playing. The lower pitch often seemed "heavier" or more substantive, and Black Sabbath were perhaps the first popular group to downtune. The practice of downtuning is now common, perhaps even standard, among metal groups.