Intersubjectivity is a term used to conceptualize the psychological relationship between people during conversation, e.g. for building a shared understanding. Ragnar Rommetveit, a Norwegian social psychologist, developed a conceptual framework for intersubjectivity, treating it as a social phenomenon and a dynamic process. One technique for increasing intersubjectivity according to Rommetveit is to issue 'anticipatory cues,' i.e. referring to common knowledge and indicating future situations where the knowledge will be relevant. This framework was adapted for online communication and applied to an analysis of the mod_perl module of the Apache Web server (an open source development project). Based on observations of 215 participants' contributions to the project's mailing list over a 6-month period, we explore how processes of intersubjectivity evolve across the developer network. We conclude with a discussion of how so-called proleptic instances in post-and-reply messages may be significant and trigger the co-construction of shared understanding.