Opening encounters are an integral element of everyday social interaction, and are essential for forming and maintaining social relationships between people. We present an abstract non-humanoid robotic object called the Greeting Machine, designed to communicate positive and negative social cues in the context of opening encounters. The design is of a small ball rolling on a larger dome, with a unique gear mechanism that supports a variety of subtle movements. Gestures were designed with movement experts, and were evaluated in the context of opening encounter, in a physical first-person qualitative study. Our findings reveal that an abstract non-humanoid robot designed with no metaphor to an everyday function, can be experienced as a positive or negative opening encounter. Furthermore, minimal movement, designed as Approach and Avoid gestures, may be enough to generate these positive and negative experiences. The potential in creating opening encounters with low Degree of Freedom (DoF) non-humanoid abstract robots is promising, due to the low complexity, low cost, and design flexibility of such devices.