This distasteful affliction, also known as a dingleberry, is an entanglement of cat turd in the cat's fur, usually in the buttock area. Furds occur most frequently in long-haired cats which are not fastidious about personal hygiene.
Fluffy's righteous furds required one person to hold her down and another, armed with gloves and scissors, to remove them from her tail and backside.
Sir William Belvoir had a penchant for sniffing the parlour maid's bicycle seat. His Butler was at a loss to describe what his master did - so used the sound that Sir William made ... Furd!