Classical ethology encourages a causal approach to animal behaviour, using Tinbergen's four questions concerning evolution, function, mechanism and development of behaviour. It sets aside the study of mental processes, which could otherwise help to unify our picture of the relationships between animal and environment. Here the steps in research focused on the psychological meaning of a peculiar behaviour in the mouse — carrying its tail — and what this implies regarding the mouse's cognitive world are given. Initial empirical observations suggested (...) epistemic choices concerning space and object notions in the mouse; this led us to go beyond the first stage in exploring the significance of this behaviour. Later experiments showed the limitations of an explanation based on a cause-effect relationship. An interpretative model integrating a phenomenological conceptual framework is proposed. (shrink)