We report on the observation of an intermediate state in the blinking of single CdSe/CdS core-shell nanocrystals. This state has a low quantum yield and connects the "on" and "off" states commonly observed in the photoluminescence blinking of individual nanocrystals. We find that the transitions between these two emitting states follow nearly single-exponential statistics. The transitions from the "on" state to this intermediate state result from changes in the surface passivation of the nanocrystal. The data are consistent with photoinduced, adsorption/desorption events that take place at the surface of the nanocrystals. The trion state leads to a reduction in photoluminescence in nanocrystals.