This paper presents a case study of a fully working prototype of the Sensus smart guitar. Eleven professional guitar players were interviewed after a prototype test session. The smartness of the guitar was perceived as enabling the integration of a range of equipment into a single device, and the proactive exploration of novel expressions. The results draw attention to the musicians' sense-making of the smart qualities, and to the perceived impact on their artistic practices. The themes highlight how smartness was experienced in relation to the guitar’s agency and the skills it requires, the tension between explicit (e.g. playing a string) and implicit (e.g. keeping rhythm) body movements, and to performing and producing music. Understanding this felt sense of smartness is relevant to how contemporary HCI research conceptualizes mundane artefacts enhanced with smart technologies, and to how such discourse can inform related design issues.