In Deep Purple lead singer Ian Gillan's autobiography, he explained that this song began as a joke: someone mentioned the classical composition "Flight of the Bumble Bee" and their organ man, Jon Lord, started playing variations around it.
"The Rat" is a reference to a drug habit - Deep Purple made occasional anti-drug references in their songs - "Into The Fire" was another.
Suggestion credit: Dougie - Delhi, India, for above 2
In Rock was the first album with the Mark II lineup of Deep Purple, which introduced bass player Roger Glover and lead singer Ian Gillan. This is the lineup the band returned with in 1984 after an eight-year hiatus.
The lyrics for "Mary, Did You Know?" were written by Christian singer and comedian Mark Lowry, after his pastor asked him to write a Christmas musical for their church. Southern gospel musician Buddy Greene later added music to his words.