Familiar to everyone, expressions such as “familiar, to familiarize, familiarity” are commonly used in reviews on HRI. Nevertheless, “the familiar” is a notion that lacks a precise definition and only rare studies tackle it directly. This paper is a preliminary study on human experience of the familiar when interacting with a robot. Which signals and elements trigger it? What are the mental and emotional states it associates with? How dependent is it on anthropomorphism and social acceptance? Can the familiar really be considered as a key-concept to study Human-Robot interaction and better understand what makes it a motivating, satisfying and socially adapted one? This research question was investigated in an experiment involving three protagonists: one robot, NAO, and two participants. The experiment was designed in a way allowing a real socially-engaging situation to occur. It investigates participants' response to an unannounced interaction with a robot consisting of two main actions: performing social greetings and handing an envelope containing the questionnaire that participants agreed to answer. The robot's behavior vary from one participant to another.