Thrii is a multimodal interactive installation that explores levels of movement similarity among its participants. Each of the three participants manipulates a large spherical object whose movement is tracked via an embedded accelerometer. An analysis engine computes the similarity of movement for each possible pair of objects, as well as self-similarity (e.g., repetition of movement over time) for each object. The extent of similarity among the movements of each object is communicated by a visualization projected on a three-sided pyramid, a non-directional audio environment, and lighting produced by the spherical objects. The installation's focus is intended to examine notions of collaboration between participants. We have found that participants engage with Thrii through exploration of collaborative gestures.