I have heard that Rabbi Mordecai Eliyahu's speed and accuracy in "mass-inspecting" etrogim are a true marvel.
My friend told me that he was able to check them at a rate of something like 1-2 seconds each, so one day they tried to trick the Rav by taking one of the etrogim he had checked already and deemed pasul and put it back in the line, and he kept at the same rate until he got to this one, looked at it and said 'already checked this one' LOL