Work has been done showing that chocolate can be dangerous for dogs. This will come as a surprise to some who feed their dogs chocolate without apparent harm but the evidence is difficult to ignore, in spite of its counter-intuitive nature.
The toxic dose of chocolate appears to vary from dog to dog but some estimates suggest that 150 g of dark chocolate could be lethal to a 20kg dog. This is not a difficult amount to achieve, if a greedy dog were to steal some Easter Eggs. Be careful how and where you store Easter Eggs in the lead-up to Easter and warn children not to leave them lying around, not to feed them to dogs and not to let pieces fall.
The damage is via the substance Theobromine.
While feeding chocolate in moderation may be acceptable, the only really safe advice is don't.
If your dog does take some chocolate, seek prompt veterinary advice. It may be that timely use of homeopathic Nux vomica might reduce the harmful effects and buy more time.