Broccoli
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Broccoli may be considered a superfood for people, but it can be deadly to your dog if a large amount is consumed as this vegetable contains a substance called isothiocyanate. This compound contains methylxanthines which can cause very serious diarrhea or gastrointestinal irritation, vomiting, seizures, irregular heartbeat, or potentially fatal anemia. The high fiber content can also cause blockage in the digestive system.