George Zimmerman's defense left court-watchers waiting until the last minute Wednesday, finishing with their last witnesses but leaving open the possibility that the former neighborhood watch volunteer might still testify in his own defense in the shooting of Trayvon Martin.

The final witness, pending Zimmerman's decision, was the defendant's father, Robert Zimmerman, who testified that it was his son who was screaming on the infamous 911 recording of the fatal altercation that claimed the 17-year-old Martin's life in 2012.

Robert Zimmerman joined his wife, Gladys, in testifying that they believe it was their son George.

By contrast, Trayvon Martin's mother, Sybrina Fulton, said she was "absolutely" certain that the panicked voice was that of her son Trayvon, with the late teenager's brother, Jahvaris Fulton, making a similar determination.

The defense team, which consumed most of the day on testimony from a "use-of-force" expert, also called one of Zimmerman's neighbors -- Olivia Bertalan -- who spoke of being appreciative of Zimmerman's support after a home invasion at her house.

In one memorable moment Wednesday, attorneys from both sides grappled with a foam dummy on the floor of a Florida courtroom, working to demonstrate to rapt jurors their competing versions of what happened the rainy 2012 night Trayvon Martin died in an altercation with George Zimmerman.

Zimmerman, 29, is accused of second-degree murder in the February 26, 2012, death of Martin, a 17-year-old from Miami who was staying with his father in Zimmerman's Sanford, Florida, neighborhood.

Defense attorneys argue Zimmerman shot Martin in self-defense after the Miami teenager charged him. Prosecutors argue he followed Martin through his neighborhood and shot him without provocation.

To that end, Assistant State Attorney John Guy brought out the dummy in an effort to demonstrate that it would have been difficult for Zimmerman to retrieve his handgun from his pocket with Martin straddling him, as defense attorneys have argued was the case.

The fatal gunshot, Guy reminded defense witness Dennis Root, was fired at a 90-degree angle into Martin's body.

"Wouldn't that be consistent with Travyon Martin getting off of George Zimmerman and George Zimmerman raising the gun and firing it?" Guy asked Root, a use-of-force expert.

"It could be consistent with any kind of movement ... We weren't there so the info that we have is George Zimmerman's statement," he said.

Later, defense attorney Mark O'Mara straddled the dummy himself, pounding the back of its head against the carpeted courtroom floor, demonstrating how he says Martin gave him the head wounds seen in police photographs from the night of the shooting.

He later asked Root -- a former police officer with extensive training in firearms and self-defense -- if it would have been possible for Zimmerman to reach around Martin's body to get at a gun located near his hip.

"Yes, sir," Root replied, minutes before Judge Debra Nelson called a lunch break.

Earlier, Root testified the apparent fight between Zimmerman and Martin went on for a relatively long time -- some 40 seconds -- and was clearly marked by a high level of fear and anxiety.

"I have personally sat there and timed it myself, where it is about 40 seconds of time. That's a very long time to be involved in any type of physical altercation," Root said.

"We have a golden rule," he told defense attorney Mark O'Mara. "If you have not successfully completed the fight, if you have not won the fight in 30 seconds, change tactics, because the tactics you are using are not working."

The testimony came as the effort to defend George Zimmerman against murder charges in the 2012 shooting death of Martin neared its end Wednesday. O'Mara said Wednesday afternoon that the defense would have two more witnesses after Root finishes his testimony.

The defense team offered no indication whether the onetime neighborhood watch volunteer himself would testify before they wrap up their case, which is expected Wednesday. A prosecution rebuttal could follow.

At the beginning of the afternoon session, Nelson questioned Zimmerman -- over the repeated objection of defense attorney Don West -- on whether he had decided to testify. He said that he had not. When asked how long it might be before he decides, Zimmerman said, "Depends on how long the recesses are."

The closely watched trial follows a national debate over the role of guns and race sparked by the death of Martin, a Miami teenager who was staying with his father in Zimmerman's Sanford, Florida, neighborhood when he died.

Zimmerman, who is Hispanic, has acknowledged shooting Martin, but has said he did so in self-defense after Martin attacked him.

Martin supporters argued Zimmerman took advantage of what they considered loose Florida gun laws to racially profile and shoot down an unarmed African-American teenager without provocation.

The incident, inflamed by a lengthy delay before charges were filed against Zimmerman, provoked protests nationwide.

Before Wednesday's testimony, Nelson dealt two blows to Zimmerman's defense, ruling they could not introduce pictures and text messages from Martin's phone or present during testimony a three-dimensional computer re-enactment of how the defense believes the altercation played out.

The photos and text messages recovered from Martin's phone include apparent references to efforts to buy a gun, as well as discussion of a fight. They won't be seen by jurors.

However, it appears that the animation could still be used during closing arguments.

The defense said Tuesday that the animation would help the jury understand how the confrontation between Martin and Zimmerman unfolded. The prosecution argued the animated re-enactment makes assumptions, and it's not based on evidence in the case.

HLN's Graham Winch, Jonathan Anker and Anna Lanfreschi and CNN's John Couwels and Greg Botelho contributed to this report.