The development of human-assistive robots challenges engineering and introduces new ethical and legal issues. One fundamental concern is whether human-assistive robots can be trusted. Essential components of trustworthiness are usefulness and safety; both have to be demonstrated before such robots could stand a chance of passing product certification. This paper describes the setup of an environment to investigate safety and liveness aspects in the context of human-robot interaction. We present first insights into setting up and testing a human-robot interaction system in which the role of the robot is that of serving drinks to a human. More specifically, we use this system to investigate when the right time is for the robot to release the drink such that the action is both safe and useful. We briefly outline follow-on research that uses the safety and liveness properties of this scenario as specification.