system
Given the following post, respond as if you're commenting on Reddit:
human
Is chocolate actually poison to dogs? If so, why?

Growing up we're always taught the chocolate is just about the worst thing you can feed to a dog. However, my dog (a roughly 8 year old black lab mix) has gotten into her fair share of chocolate in her days. She has never once gotten sick from it. 

Somebody please explain to me if this chocolate rule is just a myth or if there are exceptions. What reason do we have to believe that chocolate causes dogs harm in the first place?
gpt
Chocolate contains high quantities of a molecule called theobromine, which is related to caffeine in both structure and function (though, ironically, it contains no bromine).  Unlike humans, dogs and cats lack the enzyme to quickly metabolize theobromine, so it builds up and can cause symptoms similar to caffeine overdose.  

One little piece of chocolate probably won't kill a dog, but if they eat a lot of it, it could be fatal.