The discussion revolves around the legality and safety of transporting about a liter of deuterium oxide (D2O) in checked baggage on an American Airlines flight from Phoenix to Albuquerque. Participants generally agree that bringing D2O is permissible since it is not classified as a dangerous good by IATA or the Department of Transportation. Concerns about potential issues during security checks are raised, with suggestions to label the bottle as "NON TOXIC" and provide a contact number for inquiries. A TSA representative confirmed that while larger containers may be searched after X-ray inspection, there should be no significant issues with checking D2O. The conversation also touches on the absurdity of certain TSA regulations, particularly regarding marijuana, which remains illegal under federal law despite its legal status in some states. Overall, the consensus is that transporting D2O in checked luggage is likely to be fine, provided proper precautions are taken.