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.
That is a happy ending! My SIL's boxer ran out the door one Christmas morning at the other SIL's house. We all watched in horror as she dashed into the street and ran INTO an car. She bounced off the passenger door, and seemed completely unphased!