It's completely normal for dogs to swallow large chunks of food. In the wild, wolves tear off large chunks and swallow them whole, therefore increasing the food intake while decreasing the time it takes to eat. Many dogs still have this instict, especially if there are other animals around. As long as he isn't choking or hurting himself with this, don't worry about it. If it really bothers you, cut up the chicken before you give it to him.