The Teselecta antibodies were robotic guards inside the Teselecta. They served as security, killing anybody who did not have the correct privilege to be in their sector of the Teselecta. However, their programming would not distinguish between who they were meant to kill. The antibodies simply executed any being that registered as unauthorised at any given time- a flaw that worked against the crew of the Teselecta itself. A Nazi general was a victim of the Teselecta antibodies. They often yelled things that a doctor combined with a polite executioner might say, such as, "You will experience a tingling sensation and then death."
When Amy Pond and Rory Williams turned off the Teselecta's automatic staff notifier (their wrist device), they all teleported away, leaving Amy and Rory to be killed by the antibodies. The couple was rescued by River Song when she materialised the Doctor's TARDIS around them. (TV: Let's Kill Hitler)
The berserk antibodies are presumed to have been dealt with some time after this incident, and either reprogrammed or retired, as the Teslecta crew were able to resume use of their ship with the threat removed. (TV: The Wedding of River Song)
They were about four feet tall (miniturisation ray notwithstanding), with bulbous heads. Cables, resembling tentacles, protruded from this head, giving it the appearance of a cephalopod or jellyfish. (TV: Let's Kill Hitler)
They had anti-gravity technology and hovered in the air. They used an electric discharge from two hidden coils to disintegrate their targets and manipulated their wires to hold people in place.
The antibodies could only recognise if a person had the correct privileges by noting if they had a bracelet that glowed green. Without that device, they would politely incinerate the intruder.
They emerged from consoles in the Teselecta's hull. There were at least a dozen of them. They had access to scanner technology; they could tell that there were only two humans on board the Teselecta after the crew had beamed off. (TV: Let's Kill Hitler)