Ritual Knife

The  is a weapon added to Fallout 3 with the release of the Point Lookout add-on. It is used by the Swampfolk and can be repaired with Knives as well as the Slasher Knife and Ant's Sting. This weapon has the second lowest AP cost in the game (the first being Toy Knife, but the HP of 10 and extremely low damage makes the knife almost useless, and tied with the Alien Pulverizer), as well as a very high rate of attack. Keep in mind that the weapon has a high critical hit multiplier, making all those attacks even more effective, especially when boosted with fitting perks and equipment.

It is found in the caves beneath the Ritual Site on the sacrificing table near the book after beginning the quest The Dark Heart of Blackhall. (the caves entrance is sealed until you start the quest)

Appearances
The appears in the Fallout 3 add-on Point Lookout.