The writer of "Eyes of the Insane" and the leader of Mumford & Sons were both musicians. This band was formed in 2007.
Toms Enrique Araya Daz (born June 6, 1961) is a Chilean American musician, best known as the vocalist and bassist of the American thrash metal band Slayer. 
Marcus Oliver Johnstone Mumford (born 31 January 1987) is a British-American singer, songwriter, musician and producer best known as the lead singer of the band Mumford & Sons. 
 "Eyes of the Insane" was written by vocalist Tom Araya during pre-production for the album. 
 The band consists of Marcus Mumford (lead vocals, electric guitar, acoustic guitar, drums), Ben Lovett (vocals, keyboard, piano, synthesizer), Winston Marshall (vocals, electric guitar, banjo) and Ted Dwane (vocals, bass guitar, double bass). 
