The Ballistic Knife is a knife with a detachable, self-propelled blade capable of being ejected up to several meters away. It is used as an emergency self defense weapon used by Thor Steinbach, alongside the Taser. Unlike the Taser, which simply stuns an opponent for a short period of time, the Ballistic Knife does actual physical damage to those nightmares it is used against.
This weapon, if active as Thor's equipped self defense item, can be activated should an enemy get into melee range of him and attack. While struggling against the creature, he can draw the weapon and fire it into the monster to damage or incapacitate it. The blade can and in fact must be retrieved from the target, however, for it to be usable again in the future.
Luckily, any opponent injured or incapacitated will have code toggled that will allow the creature not to despawn, allowing the user to always return to that same creature later to retrieve the item at any point, in a matter similar to the Sword of Obedience from Silent Hill 4: The Room.