What method did Vincent use to trick others into believing he was Jerome?

The choice of using Jerome's blood is significant because it directly relates to the biological and genetic theme present in GATTACA. In the society depicted in the film, individuals are often identified and categorized based on their DNA. By using Jerome's blood, Vincent is able to present a biological sample that matches Jerome's genetic profile, effectively deceiving the DNA testing processes that are standard in this genetically-driven society. This method allows Vincent to pass as Jerome, as blood tests would be a primary method used for identifying genetic identity.

This strategy highlights the importance of genetic identity in the film's universe, where a person's worth and potential are often predetermined by their DNA. By manipulating biological materials, Vincent bypasses the rigid societal structures that dictate identity based on genetic makeup.

Other methods, such as using a social security number or changing his voice, would not provide the same level of deception in a society where DNA testing is paramount. Fingerprints, while unique to individuals, would also not be as effective since the society relied heavily on genetic identity confirmed by blood tests. Thus, using Jerome's blood is the most effective and directly relevant method for Vincent's deception in the context of the film.