Cacao Bean Mulch, by many home improvement centres, contains a lethal ingredient called "Theobromine". It smells like chocolate and is the ingredient that is used to make all chocolate -- especially dark or baker's chocolate -- which is toxic to dogs also. A dog that ingested a quantity of garden mulch made from cacao bean shells developed severe convulsions and died 17 hours later. Analysis of the stomach contents and the ingested cacao bean shells revealed the presence of lethal amounts of theobromine.
http://www.canadogs.com/Bulletin_Board.htm

Interesting. I thought it was the caffeine.

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Nadine Bielling
Moderator
Gardener Exchange Forum

The Laws of Ecology:
"All things are interconnected. Everything goes somewhere. There's no such thing as a free lunch. Nature bats last." --Ernest Callenbach

You were on the right track actually.

Theobromine belongs to a class of alkaloid molecules known as methylxanthines. Methylxanthines naturally occur in as many as sixty different plant species and include caffeine (the primary methlyxanthine in coffee) and theophylline (the primary methylxanthine in tea). Theobromine is the primary methylxanthine found in products of the cocoa tree, theobroma cacao.
http://chemistry.about.com/library/weekly/aa090301a.htm

I'm kind of surprised the dog ate the mulch. My mother used cocoa bean hull mulch when I was a kid and the dog never showed any interest. But us kids loved it. I would lay on a bale of mulch and just inhale. It was wonderful!

Marlyn