The test administered to suspected
replicants in
Do Androids Dream of Electric Sheep? and
Blade Runner. The test is presented as a series of situational questions designed to provoke an emotional response, questions such as "You are in a desert. You see a turtle, and flip it onto its back. It struggles to turn itself over. Even though you know it will die in the hot sun, you do nothing. Why?" or "Using only the good words that come to your mind, describe your mother." A machine (the VK machine) measures various physical manifestions (in the
movie and game, it measures pupil dilation) of these emotions. Since the
replicants are not
human and ostensibly have no emotions, their brains have to "fake" the responses, and thus the degree of the response or the timing of the response doesn't match how a human would respond instinctively.
In
DADoES? and
Blade Runner, the
Nexus 6 replicants have been programmed so well that it is very, very difficult to get a replicant-positive result from the VK test.