Cowbell-an idiophone hand percussion instrument used in various styles of music incuding salsa and infrequently in popular. It is named after the similar bell historically used by herdsmen to keep track of the whereabouts of cows.
More cowbell" is an American pop culture catch phrase originally derived from an April 8, 2000 Saturday Night Live comedy sketch about the recording of the song "(Don't Fear) The Reaper" by Blue Oyster Cult.
Don't question Bruce Dickinson!