
The Hug Shirt : "When touching the red areas on your Hug Shirt your mobile phone receives the sensors data via Bluetooth (hug pressure, skin temperature, heartbeat rate, time you are hugging for, etc) and then delivers it to the other person."
Somewhere between student and teacher.

"To Turn Upside Down Your Own Eyes", 1970, by Italian arte-povera artist Giuseppe Penone (image attributed to Paolo Pellion).
Still document of "Living with a Log" by artist Hugh Pocock, in which a 42-foot, 2-ton log was placed inside a private residence.  More images at http://hughpocock.net under "Projects".  Not technically a body extension, yes, but certainly an interesting clash of human scale and tree scale.