In this paper, we combine neurological and developmental evidences in order to differentiate between two levels of sharing: dyadic sharing, virtually present from birth and depending on the activation of shared representation, and triadic sharing, requiring that agents not only share a common representation, but also represent complementary perspectives. Mirror neurons are proposed as a fundamental mechanism to account for "dyadic sharing," explaining why infants are able to interact symmetrically and contingently with others from very early on in infancy. In the second part of this paper, we reinterpret the 9-month revolution as a revolution in sharedness: the transition from dyadic sharing to "triadic sharing." The neural event which renders this transition possible might be the emergence of a basic mechanism that allows the attribution of actions and intentions to their owner. We suggest two neuronal networks possibly responsible for the shift to triadic sharing.