Just to set the record straight on what potentially caused the mistrial today: Supposedly, the HC Medical Examiner, Thomas Baker, who previously testified for the prosecution, apparently heard the testimony by David Fowler yesterday, specifically in regards to Carbon Monoxide levels, and decided to investigate whether arterial blood gas data was actually taken for George Floyd at the hospital.
Prior to that, I believe the only data taken on gases in the blood was from the paramedics pulse oximeter, which read 98% oxygen saturation. The ME apparently discovered, very shortly after Fowler's testimony, that they did indeed take blood gas measurements at the hospital, and I guess the prosecution never thought to ask if this data existed, and thus they did not have it to enter as evidence before this point, even though Fowler's medical report, which was available to the prosecution before the trial, mentioned CO levels as potentially negatively contributing to GF's death.
The prosecution wanted to bring in Dr. Martin Tobin, the Irish doc for the prosecution from earlier, to counter the narrative that Fowler had set up, that CO could be a contributing factor, and have Tobin be able to supplement his claim with the medical evidence, by entering said arterial blood gas data as evidence. However, the nature of how this evidence would be introduced to court would make it highly prejudicial, (there are several reasons why: timing of introduction, not giving the defense time to prepare, etc.). Thus, the judge allowed Tobin to speak on potential issues of CO poisoning, but only in so far as giving a speculative opinion as a medical expert, no references to the new data. Which is fair, as the defense's medical expert never got to give a testimony based on actual data, specifically this data, and was gone, on a plane back to wherever. Judge Cahill warned,
"if he even hints there are test results the jury has not heard about, there's gonna be a mistrial, pure and simple."
However, based potato doctor, who I am not actually aware was informed of this arrangement, (I don't think he would willingly push this line if he knew it could throw the trial) did just that about 4 minutes into being put back on the stand. Nelson immediately objected and they had an off mic sidebar.
Ultimately, it would seem Cahill decided against following through with his warning about a mistrial. Apparently it is not as pure and simple as he warned. Your guess is as good as mine as to why.
God, this is entertaining.