Throwing (also putting and setting) the cat among the pigeons (also amongst the pigeons) is a British idiom used to describe a disturbance caused by an undesirable person from the perspective of a group.
Another use of the term is to "cause an enormous fight or flap, usually by revealing a controversial fact or secret", or in other words: to do something suddenly or unexpectedly which leaves the people worried or angry.[1][2] The key point being the making explicit a controversial or precarious paradigm or settlement.