Electrical Muscle Stimulation (EMS) offers rich opportunities for interaction. By varying stimulation parameters (amplitudes, pulse widths and frequencies), EMS can be used to either trigger muscle contractions, and so convey object affordances or guide user movements, or provide rich haptic feedback. However, the way users' experience changes with these parameters, and EMS in general, is poorly understood. Using a phenomenologically inspired interview technique, the explicitation interview, we study fifteen users' experience of EMS across 48 combinations of stimulation parameters. We synthesize the descriptions of EMS and relate stimulation parameters to categories of experience, such as 'temperature', 'motion', and 'sensitivity'. From the interviews, we explore more general topics in body-based interfaces, including the experience of control, metaphors for having your body actuated, and the relation between EMS parameters and perceived depth and location of sensations. These findings provide a vocabulary of EMS experience, and an insight into the relationship between specific parameters and associated sensations. In turn, this can help designers consider the user experience of EMS when developing interfaces.