Fireaxe

The Axe is a new Close Combat weapon intruducted in Left 4 Dead 2.

The axe has unlimited uses, and you can carry it for as long as you want. It kills all Common Infected in one hit, along with all Special Infected minus the Tank. The axe can kill a Witch if you can place a shot to the back of her head.

The axe should not be used against Boomers, for obvious reasons. It should also not be used for chasing Special Infected, despite the one-hit-kill. However, when used on a Special Infected, an "Execution Move" occurs. The axe is raised above the player's head, then brought down on the Infected. This all happens fast, just a second longer than a normal slash.

The axe is a slashing weapon, and has the ability to sever limbs. As with all Close Combat weapons, it can cause friendly fire damage to The Survivors.

Trivia

 * It seems to gather blood as it is used more. It starts as a normal looking red fire axe, but after a fair amount of usage, it shines with splattered blood.
 * The axe along with the Frying Pan can usually be found in The Parish as seen in the Left 4 Dead 2 beta footage.
 * It resembles the Pyro's fireaxe melee weapon in another Valve game, Team Fortress 2.
 * At 1:18 of this video, the Charger is hit multiple times with an axe showing that he can not be instantly killed by it.