Pretoria - The murder trial of paralympic athlete Oscar Pistorius continues in the North Gauteng High Court on Thursday.
Pistorius shot and killed his girlfriend, Reeva Steenkamp, through the locked toilet door of his Pretoria home on Valentine's Day last year.
He claimed to have mistaken her for an intruder.
On Wednesday, a sports exercise professor at the University of Cape Town told the court that Pistorius's decision to face potential danger instead of fleeing the scene was a reflex action.
"A reflex is something you don't have control over," Wayne Derman said.
Delivering his testimony, Derman, who worked with Pistorius for six years, said the athlete was hyper-vigilant.
He described hyper-vigilance as "restless looking around and a constant scanning of potential threats".
He said Pistorius was an anxious individual who had hand tremors and a sleep disorder, for which he took medication.
Derman said that during the opening and closing ceremonies of sporting events such as the Olympics, Pistorius would have exaggerated, startled responses to the fireworks.
Pistorius would cover his head and ears and cower until the noise ended.