Animal models have two different meanings. In bio-medical sciences, animal models are a certain number of species that are used to study biological/medical processes. In quantitative genetics, animal models are a statistical technique, which incorporate animal relatedness (i.e. pedigree) to mainly estimate heritability of traits. Thus, the former use indicates a system while the latter a method. I discuss unexpected connections between the system and the method, and argue that both animal models are essential for study of animal behaviour.