To a non-metal fan black and death metal can sound almost identical. However, there are subtle stylistic differences between the two. Death metal bands tend to employ greater complexity in their music and tend to have higher production values (this is because black metal bands often purposely opt for a grittier sound). Furthermore, vocals in death metal are usually "growls" (deep guttural roars), while black metal's tend to be raspier and more scream-like.
Black metal is mostly distinguishable due to its Satanic or anti-religious themes and imagery (Gorgoroth, for instance, used animal heads on pikes, animal blood and mock crucifixions during its concerts). While death metal also utilizes these themes, there tends to be a greater reliance on horror and gore imagery (most famously in the case of Cannibal Corpse), but with less anti-religious undertones. Black metal has a more fleshed-out ideology, often borrowing anti-religious and pro-individualist ideas from the philosophy of Friedrich Nietzsche.
Black metal became the subject of intense scrutiny and criticism following a series of 50 church burnings in Norway between 1992 and 1996 by devoted fans. Many of these buildings were hundreds of years old and considered historical landmarks. For this reason, the Scandanavian public has viewed black metal as more of an underground scene than death metal, which is more centered around the music itself and not so much its themes.
Followers of black metal view death metal as overly commercial, which contributed to a rivalry between the Norwegian black metal and Swedish death metal scenes. The Norwegian band Euronymous, for instance, sent death threats to more commercialized European death metal bands. Furthermore, there are allegations that a group of Norwegian black metal fans plotted to kidnap and murder members of various Swedish death metal bands.