I was sitting in the witness box, still under cross-examination, when the judge made an observation to the jury. He said, as nearly as I can remember, "You the jury, have heard two distinguished physicians arrive at different conclusions based on consideration of the same set of facts. This reminds me, "he said, " of old judge So and So, QC who defined an expert witness as a sonofabitch with a briefcase." I was speechless. So were the lawyers. There was a long pause as the jury members looked at one another and inwardly digested the lord's remark. After the fact, I thought of many clever things I might have said, but the judge is Master of the Court and contempt towards it is not easily undone.
To anaiyze, we often place a jury in a difficult situation when evidence of both witnesses may be equally persuasive. Medicine in many instances is not an exact science. As you may expect this observation swung the scale and the plaintiff received a large settlement. The defense had the basis for appeal on possible grounds of judicial bias but did not do so.
In retrospect the judge may have been expressing a frustration many judges and juries do have and that is having to choose between testimony they believe is conditioned by "who pays the piper calls the tune". In fact, having reviewed many such scenario's the truth that is much more usual is "the payer {lawyer} shops for those pipers{doctors} whose tune he knows he can dance to." Judges should know this of course since lawyers judge shop as well as witnesses. It's a question of shopping, not collusion and is not really mystifying.