My cat ate a piece of my granola bar and now has soft stool — could the granola have caused this?

Yes, granola can easily upset a cat's stomach, leading to diarrhoea or gas. It's not typically poisonous, but the high fat, sugar, and fiber are hard for cats to digest, and some bars contain raisins or chocolate which are toxic. Withhold any more people food and ensure your cat drinks water to prevent dehydration. If the diarrhoea persists beyond a day or your cat acts lethargic, a vet visit is a good idea to rule out other issues.