A cat's farts can smell bad for a variety of reasons, such as:
1. If a cat's food contains chemical additives and artificial flavorings, it can lead to indigestion, increased gas production, and flatulence.

2. When there are too many harmful bacteria or too few beneficial bacteria in a cat's gut, it can lead to an imbalance in the gut microbiota. This imbalance can interfere with the normal digestive process, increase gas production, and cause the cat's flatulence to have an unpleasant odor.