Pistorius, a double-amputee Paralympian, repeatedly vomited into a bucket as the pathologist testified about how the bullets fired from Pistorius' 9mm Parabellum were designed to exact maximum damage on their target, Britain's the Daily Telegraph reported.
Gert Saayman said the Ranger bullets were designed to "open up, flatten out and mushroom when striking human tissue," much as a flower would bloom.
Prosecutors maintain Pistorius deliberately shot and killed Steenkamp, a model, when he fired his gun at a closed bathroom door on Feb. 14, 2013. Pistorius maintains he thought he was shooting at an intruder.
Before Saayman began testifying, Judge Thokozile Masipa ruled his testimony on the autopsy would not be broadcast, SABC reported. When Saayman argued against broadcasting his testimony, he said his "graphic details of the injuries have the potential to compromise the dignity of the deceased" and could "harm the rights" of Steenkamp's friends and family.
The judge also banned posting details of the autopsy report on Twitter.
Also Monday, a security guard at the gated community where Pistorius lived in Pretoria defended his account of phone calls made minutes after the shooting, the BBC said. Pieter Baba said he phoned Pistorius, not the other way round as the defense team suggested.
Baba earlier testified he called Pistorius after neighbors reported hearing gunfire and was told by the defendant, "Everything is fine." Baba testified Pistorius called him back a few minutes later and was crying.
Barry Roux, Pistorius' defense attorney, suggested Monday his client had called Baba first and not the other way round, but Baba did not sway from his original testimony, the BBC said.
The trial adjourned until Tuesday.