Just thought I would post some interesting links to info about chocolate and dogs:

A 7 week old puppy weighs approx 1KG. A fully grown cairn weighs about 4-8KG.

Please see this page for information about the amounts of chocolate that can be poisonous:

• 60g per kg of body weight for milk chocolate.
• 30g per 1.5 kg body weight for semi-sweet chocolate.
• 30g per 4 kg for cooking chocolate.

The article link to above also points out that grapes and onions can be toxic to dogs too.