No chocolate. Some owners think of this as a treat to reward their pet, but it is a proven scientific fact that chocolate is poisonous for dogs and can sometimes even cause a fatal reaction. Why? Chocolate contains two substances which are toxic for dogs: caffeine and theobromine. Symptoms vary depending on the quantity eaten. The most common effects are restlessness, increased urination, rapid heart rate, asthmatic attacks, bloating, gastro-intestinal distress, severe thirst and increased body temperature. It has been reported that as little as 400mg of theobromine can be toxic if ingested by a dog weighing below 5kg. Dogs are hypersensitive to theobromine because, unlike many other animals, they are unable to excrete it rapidly from their systems. Commercial brands of sweetened chocolate contain approximately 1.5mg of theobromine per cubic centimetre (cc) while unsweetened varieties can have as much as 13mg/cc.