Just found this:
Occasionally, a cat will then stop wanting to eat normal cat food, and they make it clear to their owner that they want nothing other than raw liver. In the short term, this may be fine, but after a few weeks, serious problems can arise. Liver contains high amounts of Vitamin A, which is good in small doses, but which can be toxic if consumed at high levels. If cats eat liver every day, they soon start to suffer from a condition known as Hypervitaminosis A. The bones of their back start to fuse together, causing a painful arthritic condition. These cats are often so addicted to liver that it can be very difficult to make them eat anything else. In extreme cases, they may even need to be fed normal food through a tube until they can be persuaded to start eating a standard diet again.