So today in the Zimmerman trial, the prosecution called an expert witness, Dr. Rao, who examined the evidence of Zimmerman's injuries on the night of Martin's death and testified that Zimmerman's injuries were "insignificant" and "not life-threatening." Also, I believe she was strong for the State when she testified that the injuries were not consistent with the head being hit with a great deal of force.
I was puzzled by O'Mara's cross though. I get that you want the witness to testify that those injuries could be consistent with numerous scenarios. But, why not challenge her on her methodology? It takes me back to the Casey Anthony trial, when the State brought in, what I thought, was a lot of junk science (the dog sniffing cadavers, and the chlorine sniffing machine) and the defense did a good job of demonstrating that it was junk science.
The State is introducing this testimony for two reasons: 1.) to prove that Zimmerman was not suffering life threatening injuries which would justify deadly force, and 2.) to prove that Zimmerman is lying about his account of the altercation that night. I do not think the defense did a good job in rebutting on each of these points.
At the same time, I think people give to much weight to expert testimony, especially when it is something lay people can understand. I think, generally, most people can look at Zimmerman's injuries and determine whether they were life threatening. I think most people can determine whether his injuries are consistent with someone who has been pummeled and has had his head bashed repeatedly on the sidewalk.
I don't need an expert - though it helps. I think what harms the defense is that Zimmerman did not have a concussion or extensive bruising which seems likely if someone has had his head bashed several times. As a bald individual who shaves his head, I can tell you that a knick to my scalp causes a great deal of bleeding that runs down.
This may be tasteless, but go back and look at the pictures of Rihanna after Chris Brown beat her or think of victims who have been attacked - their injuries are far more severe than Zimmerman - and they look worse a few days later. You just don't see that with Zimmerman. Heck, you cannot even see the black eyes the next day when he does the walk through - another reason why the State played those tapes.
You will have dueling experts on the extent of Zimmerman's injuries that night, but jurors will, ultimately, see for themselves whether those injuries are that bad and are consistent with the story as described by Zimmerman. (O'Mara's attempt to say it is just exaggeration is not helpful).