Cat among pigeons

To set the cat among pigeons is to cause a disturbance as indeed a cat would if it was put into a dove or pigeon cote. The origin is obscure but someone, sometime, must have set a cat among the pigeons and observed the resulting mayhem. Some sources say that British troops in India deliberately put cats among pigeons and would then bet on how many pigeons the individual cat would kill, but this particularly distasteful origin has not been confirmed by reliable sources. The expression has been used figuratively since the early 19th century.