This paper presents a case study that explores the effectiveness of parallel conceptualization efforts to expose potential requirements issues in rapid prototyping. The case study consists of developing and comparing five design alternatives to model the safety-critical computer assisted resuscitation algorithm (CARA) software for a casualty intravenous fluid infusion pump using a set of computer aided Software Engineering Automated Tools (SEATools). The prototyping effort showed that users can efficiently create / modify multiple parallel models and reason about their complexity using SEATools. The study also illustrates the usefulness of comparative rapid prototyping to identifying strengths and weaknesses of alternative designs, improving the final result. The case study also exposed numerous omissions and discrepancies in the requirements document and highlighted useful future enhancements for SEATools.