Prosecutor Gerrie Nel asked sports and exercise medicine Professor Wayne Derman whether the shooting would still have happened had Pistorius only experienced one startled response from a noise in his en-suite bathroom that night.
Derman said there would need to be more than one because of the period of time that lapsed between the startle and going to get the firearm.
He said the physiological response to the noise would diminish after some time if a second startle was not stimulated.
On Wednesday the professor described Oscar Pistorius as an anxious individual who had hand tremors and a sleep disorder which Derman had to medicate.
He said that during the opening and closing ceremonies of sporting events such as the Olympics, Oscar Pistorius would have exaggerated startled responses to the fireworks.
Oscar Pistorius would cover his head and ears and cower until the noise ended.
Derman worked with Oscar Pistorius through assessments, consultations and as part of the South African team at the Beijing and London Olympics in his capacity as a physician.
On Thursday Derman said that after an individual experienced a startled response, the body immediately kicked into fight or flight mode.
He said once an individual was in that mode, the blood flow to the cognitive thinking part of the brain decreased, diminishing one’s thinking capacity slightly.
Earlier, Nel asked Derman whether he had taken notes when Oscar Pistorius had told him what happened on the night he shot dead his girlfriend Reeva Steenkamp.
Derman said he had not.
“Is it not the responsible thing to do to take notes of what was said?” Nel asked.
Derman said he could not recall the date he had recorded what Pistorius had told him about the incident.
“It must have been when the trial had started, I cannot recall the exact date.”
He said he met Oscar Pistorius for a second time to clarify some details he did not understand.
“I felt it was important for me to gain understanding of exactly what happened. If I had any doubt of my feelings then I would not be standing here.”
When Nel began Derman’s cross-examination, he called the physician’s objectivity into question.
Nel said as Pistorius’s doctor Derman was bound by the Health Professions Council of SA (HPCSA) regulations to act in the best interest of his patient.
“Is that what you’re doing now?” Nel asked.
“I believe so,” Derman replied.
Nel said if Derman were to be objective, his testimony could harm his patient.
“I disagree. I am not going to come before court [with] a biased report because I have been very careful to back up my report.”
When asked if he would give evidence against Pistorius, Derman said: “I’m under oath, I have to provide the truth and that is what I’ll do”.
He said he had been careful and measured when compiling his report and consulted with his lawyers to make sure that he had not breached any HPCSA regulations.
Pistorius is charged with murdering Steenkamp on February 14, 2013.
He shot her through the locked door of the toilet in his Pretoria home, apparently thinking she was an intruder about to open the door and attack him. She was struck in the hip, arm, and head.
After firing the shots, Pistorius used a cricket bat to break open the door to get to a dying Steenkamp.
He has pleaded not guilty to the charge of murder and to three firearm-related charges.
The State argues he killed her during an argument.