I haven't ever had that happening to me but one of my friends had to witness her cat kill her fish. It's a big cliche but it's just because of her own carelessness. She accidentally left open the top part of her aquarium, and somehow her cat climbed on top of the whole aquarium without her noticing that. One thing led to another and before she could even realise, one of her goldfishes was gone. Even when my friend does love her animals, for her it's more of a laughable thing nowadays. She knows she should've been more careful with the lid on top but at least she now knows to check twice not to leave it open.
