The entry into symbolic communication through language, gesture or visual signs is one of the key moments in the mental and social development of infants. It is the point from which they start to have a much better social interaction with their parents, other children and adults, and can begin to observe the massive achievements of cultural accumulation. The question addressed in this paper is how developing robots could autonomously make this important transition in their mental development. Based on observations of the way human infants bootstrap into symbolic communication, we propose that gestural symbolic communication comes before auditory symbolic communication and is discovered through a process of ontogenetic ritualisation. The paper identifies the nature of ontogenetic ritualisation and reports on first experiments to achieve this form of learning in humanoid robots.