We explore sketch-based trajectory retrieval in virtual reality (VR) as a method for analyzing dense 3D motion data. Using a flotation simulation—an industrial particle separation process in which rising air bubbles collect material in fluid mixtures—as a challenging testbed, we investigate how immersive sketching can support visual querying and hypothesis exploration. Our tool allows users to sketch query paths directly in 3D space to retrieve similar motion patterns. Structured tasks and expert feedback reveal both the potential of this approach for exploratory trajectory analysis and its current limitations in precision and adaptability.