This paper seeks to outline methods underlying the development of the Xth Sense project, an ongoing research which investigates exploratory applications of biophysical sound design for musical performance and responsive milieux. Firstly, an exploratory study of the acoustics of body sounds, namely muscle sounds is illustrated. I describe the development of an audio synthesis model for muscle sounds1 which offered a deeper understanding of the body sound matter and provided the ground for further experimentations in signal processing and composition. Then follows a description of the development and design of the Xth Sense - a wearable hardware sensor device for capturing biological body sounds, this was implemented in the realization of Music for Flesh I - a first attempt at musical performance. Eventually I elaborate on the relations between the role of sound in cognitive experience and the acoustic capabilities of biologic body sounds and try to establish an array of principles which will provide the backbone of the next stage of my inquiry.