The Aching family cat. Ratbag would aspire to be a Greebo, if he wasn't so fat and idle. Nominally the Aching farm mouser, Ratbag also sees his remit as involving a one-cat war on anything with wings and feathers. Tiffany deplores this, and the Nac Mac Feegle oblige her with some behavioral psychology to train the cat out of its avicidal mentality. This involves a Feegle dressing up in bird costume, offering itself as bait, and then repeatedly nutting the cat until it gets the idea.
Reminiscent of B.F. Skinner's famous learning experiments with pigeons, which he trained to head-butt appropriate levers to obtain rewards and avoid disincentives. This is the Skinner experiment with attitude.