Waterways are a mess of molecules, presenting a massive challenge for researchers trying to understand how marine life communicates chemically. But with an assist from analytical chemistry, researchers from Georgia Institute of Technology have now solved an underwater mystery: what chemical cues mud crabs use to avoid predatory blue crabs (Proc. Natl. Acad. Sci. USA 2018, DOI: 10.1073/pnas.1713901115).