For expert evidence to be tested, a thorough understanding of the evidence is critical. Experts are privileged in that they are able to give evidence, on more than what they have directly observed, and they have the power to influence a judicial decision. For an expert opinion to be successfully challenged, its weaknesses or flawed logic need to be identified, and a thorough understanding of the medical topic is required. Achieving this is not straightforward, as what is being said appears to be based on impenetrable material.