If they do, it could be because they want to feel more like part of the family, or it's just a particular animal's personality and that animal was matched with the person meant for it.
If it's commercially made chocolate, they'd have to eat a lot to get sick. If it's 'real' chocolate, a little amount can be sufficient to really make them sick. Commercial chocolate is a lot of fake stuff.
I saw this show for the first time last night. I didn't think it was sad, because the nice doggy gets adopted into a home where the people have been evaluated and dog is placed with people who are best suited for the individual dog. It's like a reality game and they all know only one home gets the dog. The people know they might not get that dog. But I'm glad that the people who don't win on the show, will probably adopt and rescue another well deserving dog. Just my take . . . but I only saw the one show.
I love this! I'm just going to add one more to my version before using it–next to last item--I can legally spay/neuter them so they don't get (or get anyone) pregnant!!!