This kitten was taken from its mother at a very early age. As such it is incredibly frightened of the new world, when just a few days ago it was in the safety of its mother's womb. Today its mother is nowhere in sight and there is no one to call 'mother'. The dog however serves as a useful substitute and instead of eating the little kitten whole, it nourishes and trains the cat.
Just observe how the cat tries to hold on to the protective body of the dog with its frail paw. It still has its guard up because its ears are pointing in the upward direction, this makes up for a very concerning sight. The cat has probably been through rough times as a tiny creature still learning to trust the world.