Chocolate contains two toxic compounds called caffeine and theobromine. Humans have a higher tolerance and rarely suffer form chocolate poisoning. The theobromine concentrations vary in different types of chocolates - it's easiest to remember that the darker the chocolate, the more dangerous it is.

Symptoms of chocolate poisoning in your dog are;

• Increased heart rate 
• Increased/inappropriate urination
• Shaking
• Seeming agitated
• Vomiting
• Diarrhoea
• Erratic Breathing
• Seizures/Collapse (if left untreated)

For cats - chocolate is usually more toxic, but since they can detect the sweetness, they are very unlikely to consume it.