Which method should never be used to identify an unknown substance?

Using taste as a method to identify an unknown substance is unsafe and not a valid practice in forensic science or any other scientific field. Tasting a substance could lead to harmful consequences, including poisoning or adverse health reactions, due to the potential for toxic or caustic substances being present. Proper identification of unknown substances should be conducted through reliable methods such as chemical analysis, spectrometry, or other scientifically validated techniques.

While the other options may involve using the senses to gather preliminary information, they also have risks and limitations; however, taste stands out as the most dangerous and inappropriate choice for substance identification. Therefore, relying on taste poses significant health risks, making it unacceptable in the context of properly identifying unknown substances.