take a very small dog and a large quantity of them to do real harm. But basically they take a really long time to remove the theobromine from their blood and that stuff behaves like caffeine. So it's like taking way too much caffeine and having the effects for hours to days. And by way too much I mean enough to cause hyperactivity, seizures, etc.

That's why if they eat a large chocolate bar you could start to have issues. Especially a small dog.