A traumatized Vulcan crew member who murders station personnel with a prototype rifle because he hates seeing them laugh.
Chu'lak is a Vulcan serving on Deep Space Nine in Field of Fire and one of only six survivors of a ship destroyed in the Dominion War. He becomes a killer, shooting officers in their quarters with a TR-116 rifle fitted with a miniature transporter that beams each bullet straight to the victim.
Ezri Dax summons the memories of Joran to profile the murderer and realizes the victims all kept photographs of people laughing. Joran identifies Chu'lak, and in a final standoff Ezri shoots first, wounding him and calling for medical help instead of killing him.