  We investigate the physics of an optically-driven micromotor of biological
origin. A single, live red blood cell, when placed in an optical trap folds
into a rod-like shape. If the trapping laser beam is circularly polarized, the
folded RBC rotates. A model based on the concept of buckling instabilities
captures the folding phenomenon; the rotation of the cell is simply understood
using the Poincar\`e sphere. Our model predicts that (i) at a critical
intensity of the trapping beam the RBC shape undergoes large fluctuations and
(ii) the torque is proportional to the intensity of the laser beam. These
predictions have been tested experimentally. We suggest a possible mechanism
for emergence of birefringent properties in the RBC in the folded state.
