1) Lucy learns from her mom that chickens lay eggs because they are birds, and birds are a type of species that lays eggs. 2) Mammals like Lucy and her dog Roger give live birth to young, while other animal groups like birds, fish, amphibians, and reptiles lay eggs. 3) There are five major animal groups - mammals, birds, reptiles, amphibians, and fish. Birds have feathers and warm blood, while fish, amphibians and reptiles are cold-blooded.