The recent leak of a video purporting to be of the retail version of Black Ops 2 revealed a number of new details about the game, including the much-talked about but never revealed crossbow weapon.
The video itself is more than likely to belong to a stolen copy of Black Ops 2's Gamescom build, and not the full retail version of the game, but it contains more than enough new details for us to look at and dissect for information.
Among them is the aforementioned crossbow, which appears to be semi-auto (obviously) and equipped with an ACOG scope for aiming assistance. The weapon has been entirely redesigned for Black Ops 2 and appears to be a one-hit-killer. Granted, there's a brief amount of travel time with the bolts it fires, so it has to be balanced accordingly.
Curiously, the weapon appears to be equipped with explosive bolts, so there's a slight delay before the player gets the kill, with a slight flash beforehand.