The paralympian sat alone in the dock listening to the testimony of the first witness, University of Pretoria construction and economics lecturer Michelle Burger.
When the lunch break was announced Pistorius looked at his watch, got up and walked out alone, shaking hands with a few people along the way.
Burger testified, in questioning by prosecutor Gerrie Nel, that the morning of the shooting, she went to work as normal and told a colleague about the screams and gunshots she had heard from a nearby house at 3am.
Only later, when her husband called her, did she learn that Pistorius had shot dead his girlfriend Reeva Steenkamp.
Burger, who spoke in Afrikaans, at times had to help the large, blonde woman trying to translate her testimony into English, sitting next to her.
Burger corrected her and used her broken English to make her point.
The State will try to prove that Pistorius committed premeditated murder when he shot and killed Reeva Steenkamp through a bathroom door in his Pretoria home on February 14 last year. In addition he is charged with illegal possession of a firearm and ammunition.
His lawyers will argue that he mistook her for an intruder when he shot her.