Complex sentence: Littlefoot notices a longneck herd entering Great Valley and informs his grandparents, who tell him that the longnecks are their cousins and that they must go and greet them.
Split into simpler sentences: Littlefoot notices a longneck herd entering Great Valley, and informs his grandparents. They tell him that the longnecks are their cousins, and that they must go and greet them.