Sensitising, having participants reflect on their experiences with a topic before a research session, has been a core principle in design research for two decades. Yet attempts to put this principle to a direct test have been limited. This study provided a first quantitative test in a longitudinal conversational survey, conducted via WhatsApp among 118 employees of four Dutch organisations. Respondents were assigned to a condition that received short pre-messages inviting them to think about the topic of an upcoming question, or to a control condition without pre-messages. Two outcomes were examined across 1,247 respondent-question observations: response length in words and item nonresponse. Bayesian hierarchical models with informed and uninformed priors were estimated, using actual exposure to a pre-message as the predictor. For response length, Bayes factors provided moderate evidence for the null hypothesis (BF₁₀ = 0.14–0.22), with posteriors centred near zero. For response probability, the evidence anecdotally favoured the null (BF₁₀ = 0.37–0.45). Here, a practically relevant effect was neither demonstrated nor ruled out. Pre-messages in this passive, unverifiable form showed no demonstrated benefit. Future tests of sensitising should employ preparatory exercises whose uptake is observable.