The readback/hearback loop is a communicative protocol used in many high-risk environments to ensure that a verbal instruction has been heard correctly by a receiver. However, it does not necessarily ensure that an instruction has been understood. Using an international sample of hydroelectric power generation controllers, this study examined whether particular linguistic (complete and partial readbacks) and prosodic (final intonation, filler, and interturn delay) cues contained within a readback response could signal to listeners the extent to which speakers had understood an instruction. The results indicated that different prosodic cues are used to detect nonunderstandings, depending upon the linguistic content of the readback. The results have implications for training and system design in distributed environments.