Normal feline faeces are brown and well formed. If a cat is suffering from diarrhoea, the faecal consistency becomes soft or even watery, and the colour may also change to lighter or darker than normal. There may also be fresh blood or mucus in the faeces. The cat's pattern of defecation will also change and the cat may strain on the litter tray. These are important signs to look out for and will help in determining the cause of the diarrhoea.