Neighbor Michelle Burger told the court she heard two people -- a man and a woman -- shouting, as well as "bloodcurdling screams" coming from Pistorius' home in Pretoria, Britain's the Guardian reported.
"The fear in that woman's voice -- you only fear like that if your life is threatened," Burger testified, noting she heard four gunshots.
Pistorius, a double-amputee Paralympian, has pleaded not guilty to murder and weapons charges in the death of his model-girlfriend Reeva Steenkamp, who was shot through a door and killed Feb. 14, 2013. He said he thought an intruder had broken into his house and was in his bathroom when he fired.
Before testimony began, presiding judge Thokozile Masipa asked Pistorius if he understood the charges against him and to enter a plea, SABC reported.
"Do you understand the charges Mr. Pistorius?" Masipa asked.
"I do my lady," Pistorius responded.
"How do you plead?" the judge asked.
"Not guilty, my lady," he said.
The start of the trial -- portions of which will be broadcast live -- was delayed because of the unavailability of an Afrikaans interpreter, SABC reported.
Another interruption was caused by a woman known only as Anna Marie, who has maintained Pistorius needs psychiatric evaluation before the trial proceeds. The woman, who claims she has known Pistorius since he was a child, made a similar disruption last fall.
The trial adjourned until Tuesday.