We present results of a case study looking at how domain knowledge is communicated to developers using executable acceptance test driven development at a large software development company. We collected and analyzed qualitative data on a large software development team's testing practices and their use of a custom-built executable acceptance testing tool. Our findings suggest that executable acceptance tests (1) helps communicate domain knowledge required to write software and (2) can help software developers to communicate the status of the software implementation better. In addition to presenting these findings, we discuss several human aspects involved in facilitating executable acceptance test driven development.