The painstik is a Klingon ritual instrument that delivers intense pain, used in rites such as the Age of Ascension and the ceremony confirming a leader's death.
Klingons use painstiks to test a warrior's courage. In the Age of Ascension, a warrior walks between lines of comrades who strike with painstiks while the warrior declares his feelings, enduring the pain as a proof of strength. Worf's crewmates recreated the rite on the Enterprise-D holodeck in 2365 to mark his tenth anniversary.
They are also used in the Sonchi ceremony, in which the death of the Klingon chancellor is confirmed by jabbing the body. This was performed after K'mpec died in 2367.