The appearance of a robot is generally understood to affect human perception of the robot, yet the majority of investigation into the impact of robot form has focused on humanoid robots and robot size. To better understand the impact of less anthropomorphic morphological characteristics, we present an exploratory study on the impacts of variations in concavity and edge roundness on human perception of robot arms. We systematically varied robot arm stimuli to span three levels of concavity and three levels of edge roundness, before conducting an online, survey-based, within-subject study ( \(N=157\) ) to investigate the impact on perceptions of social characteristics, safety, and expected price. The results show that concavity significantly impacts discomfort and price sensitivity, with participant preferences split on whether “thick” or “thin” arms are preferable for in-home use. The results of this work can inform roboticists and designers looking to develop new systems or when choosing robot systems for in-home tasks.