At least partially artificial, the probic vent took the form of a small metallic tube entering the back of the Sontaran's neck. This vent was normally used by the Sontarans to feed directly on energy to "recharge" rather than eating. Raw plasma was fed into the vent to nourish them. (COMIC: The Betrothal of Sontar) Sontarans did not consider this a weakness however, since it meant that they must always face their enemy in battle, nor could they be cowardly or retreat. (TV: The Time Warrior, The Sontaran Experiment, The Sontaran Stratagem)