What does the turnstile at GATTACA do to those entering?

The turnstile at GATTACA is designed to collect a blood sample from individuals entering the facility. This is significant because the society depicted in "GATTACA" places a strong emphasis on genetic identity and predispositions. By pricking the finger and obtaining a blood sample, the system can analyze the genetic material to assess the individual's DNA, allowing for the identification of genetic makeup, potential health issues, and social status.

This method fits within the broader themes of the film, which critiques the ethical implications of using genetics to determine a person's worth and opportunities in society. The act of taking a blood sample is a direct way to establish one’s genetic identity, which is central to the storyline and the societal norms represented in "GATTACA." Other options suggest different forms of identification or biometric scanning that may not have the same direct link to the characters' genetic analysis as the blood sample does, making the choice of a blood sample both pivotal and resonant with the film's themes.