Evolution of C iiλ6580 and λ7234 features in the spectral time series of SN 2011fe. Two axes depicting blueshift with respect to 6580 Å and 7234 Å are overlaid, with velocities given in units of 10³ km s^-1. C iiλ6580 begins as a notch which gradually recedes in velocity and weakens progressively until it is difficult or impossible to reliably identify at +6.7 d. C iiλ7234 follows a similar evolution, but disappears by −1.3 d.