Oreos don't actually contain real chocolate, only chocolate flavouring, so they aren't dangerous.

My dog Leather ate an ENTIRE McCain chocolate cake, we didn't even get a bite, but it was a cake, and cakes don't contain real chocolate either, so she didn't even get sick..

I've given Timber small pieces of white chocolate, and I've rubbed real chocolate on my hand so it tastes and smells like it, but it's not there...

I don't make it a habit though, if they get a taste for it, they'll like it forever. I've read some interesting reports on the internet that say dogs generally don't even like that taste of chocolate once they are old enough to decide what they do or do not like. It's usually when they are puppies that they develop a liking for it and never stop liking it