Nel was cross-examining Pistorius in the High Court in Pretoria on his claim that he heard a noise from inside the toilet seconds before he pumped four bullets through the closed door.
“I heard wood moving. I think I heard the door opening,” Pistorius said, keeping his eyes fixed on Judge Thokozile Masipa.
“Not once did you say ‘I heard a door opening’… it’s not in the [court] record. Why now?” Nel asked.
According to Pistorius he was in his bathroom, gun held out in front of him, looking between the open window, through which he claims an intruder entered, and the toilet door.
He has been charged with murdering his girlfriend in his Pretoria home shortly after 3am on February 14 last year.
He shot Steenkamp through a locked toilet door, saying later he mistook her for an intruder about to come out and attack him.
Pistorius said he got out of bed shortly before the shooting to bring in two fans from his balcony. Steenkamp apparently got out of bed without him noticing and went to the bathroom.
Pistorius heard the bathroom window sliding open, got his gun and went towards the noise.
He then heard the toilet door slam shut. After he peered into the bathroom and seeing nobody there, he thought the intruder was in the cubicle.
“I heard a noise which I perceived to be somebody coming out,” the athlete said.
“But it [the noise] could have been anything,” Nel countered.
“The hearing of a noise and the perception that you are being attacked is two different things,” Nel said.
The trial was postponed to Monday.
Pistorius is also is also charged with three contraventions of the Firearms Control Act, one of illegal possession of ammunition and two of discharging a firearm in public.
He allegedly fired a shot from a Glock pistol under a table at a Johannesburg restaurant in January 2013.
On September 30, 2012 he allegedly shot through the open sunroof of a car with his 9mm pistol while driving with friends in Modderfontein.
Pistorius has denied guilt on all the charges.