The syringe is an item only used by the spy. The Spy inserts deadly poison in the syringe, and since he can't punch (but can tie up) it's his only silent weapon. One dose of poison can make an enemy soldier dizzy, two can knock him out, and three can kill him. The poison captules can be found in cupboards, drawers etc around the map. The syringe can be used from behind and in front of an enemy soldier (only in Commandos 2 and 3) while the Spy in Commandos Strike Force does not carry a syringe, but only other means of silent knocking out tools.