Probic vent

The Probic vent was a part of all cloned Sontarans. At least partially artificial, it took the form of a small metallic tube attached to the back of the Sontaran's necks. This vent was normally used by the Sontarans as a way of directly feeding off energy to "recharge" rather than eating (as the latter was slower). The Vent was also a major weakness, since a blow to the Probic Vent could knock a Sontaran unconscious or even kill them. (DW: The Time Warrior) A lesser blow could cause them pain and/or stun them (DW: The Sontaran Stratagem). An arrow (DW: The Time Warrior) or a thrown knife (DW: The Invasion of Time) would almost certainly prove deadly. The Sontarans did not find it a problem, however, since it meant that they must always face their enemy in battle and could not be cowardly and run away. The Tenth Doctor momentairily disables General Staal using a Tennis racket and a ball by rebounding the ball from Staal's Teleport pod into the Probic Vent. (DW: The Sontaran Stratagem)