put (or set) the cat among the pigeons say or do something that is likely to cause trouble or controversy. British
☞ This expression was first recorded in John Stevens's New Spanish and English Dictionary (1706), where it is explained as referring to a man coming into the company of a group of women. The idiom flutter the dovecotes (seeflutter) is based on the same idea of a group of pigeons as a tranquil or harmless community.
2000Adrian HastingsOxford Companion to Christian Thought John put the cat among the pigeons by establishing in 1960 a new Roman Secretariat of Christian Unity.