Doubt has been raised about the validity of results that appear to demonstrate sex differences in the type of infidelity that elicits jealousy. Two studies explored proposed methodological weaknesses of this research. The first study distinguished participants who had experienced infidelity and those who had only imagined infidelity. The study found the classic sex differences when participants were “forced” to choose which kind of infidelity would be most upsetting, and these differences were more pronounced among participants who were recalling the actual infidelity of a partner. The second study explored the impact of the relatively brief, perhaps cursory response that is commonly evoked by questionnaires versus a slower, more vivid imagining of the infidelity experience. The classic forced choice results were found, and the vivid imagining produced effects that are more powerful. The overall results suggest that participants who had experienced infidelity or vividly imagined infidelity showed greater sex differences, suggesting that the usual format (filling out a questionnaire) may not trigger the evolved mechanism for jealousy.