A popular law reform solution to the problem of scientific evidence is to enhance the gatekeeping function of the judge. This is typically to be done by training judges to apply a reliability test, i.e. a set of criteria for determining whether the evidence being presented is reliable and valid. Although broadly supportive of this solution, this article argues that it must be approached with the right attitude and the right tools. The article aims to provide both. In terms of attitude, it argues that critical engagement with the nature of scientific inquiry is essential, not just in aiding the fact-finding mission of the court, but in maintaining the integrity of a liberal democratic system. In terms of tools, it aims to illustrate the basic theoretical and methodological grounding that is needed for critical engagement. It does so by eschewing an abstract and theoretical discussion, and focusing on a specific case study, namely: the use of brain-based lie detection evidence.