Chocolate can be bad because it contains theobromine. Theobromine, in high amounts, can be toxic. Of course milk chocolate is the most dilute and will contain less theobromine than dark or baker's chocolate. It also depends on weight and how much was ingested, and just your individual dog. A little usually doesn't hurt, but you never know, and just to be safe keep it all out of reach

Apple seeds are also bad!