哀車の術 is one of the five emotional jutsu (五車の術) that manipulate a person feeling of surprise「喜車」、anger「怒車」、sadness「哀車」、happiness「樂車」、fear「恐車」. The practician is trained to have his/her 5 emotions removed. With these emotion removed, he can read the surroundings of the opponents and through words he can freely kill them by controlling their emotions.
Long story short, 哀車の術 might be used to manipulating sadness?