In the movie, “The Right Stuff”, there is a scene where Alan Shepard (played by Scott Glenn) is being tested along with the other astronaut hopefuls, wherein a needle is injected into the meaty part of his hand between his thumb and forefinger. Said needle is apparently attached to some kind of electrical device. Presently, his forearm begins to twitch uncontrollably. Shepard says to the technician, “why are you doing this?” The technician replies along the lines of, “it would be too difficult to explain”.
What was going on here?