The increasing presence of mobile robot emphasizesthe crucial need of robot interaction skills. In this paper, we introduce eight prosody-only utterances as nonverbal communication sounds representing various speech acts (greeting, farewell, gratitude, apology, warning, prohibition, indirect request, direct request) with two subjective evaluations: i) an audio evaluation test and ii) a video evaluation test. The results from the first study show that nearly all prosody-only utterances were correctly understood as intended speech act. A subset was selected for a second study, where the overall results showed a general tendency of understanding that the robot was requesting human to yield the navigation passage regardless of the actual intent. This paper aims to advance robots’ nonverbal sounds towards human language, highlighting prosody’s role in signaling request intent in human-robot interaction.