In Killer Queen, just as Freddie was about to sing the next verse ("to avoid complications..."), Brian already started the solo. Freddie picked it up quickly though and just mumbled some of the words before carrying on with the show.
Freddie Mercury (lead vocals, piano, tambourine),
Brian May (electric guitar, backing vocals, banjo),
Roger Taylor (drums, backing vocals),
John Deacon (bass guitar, triangle)