There is one secret trophy in Call of Duty: Black Ops for the PS3.
The trophy is bronze and it is called See Me, Stab Me, Heal Me, and the details are as follows: Fire a Pack-a-Punched Ballistic Knife at a downed ally to revive them from a distance.
This is referring to a weapon in the Presidential Zombie Mode, which can be unlocked by completing the game on any difficulty, or byusing a code on the computer terminal. You need to use the Pack-a-Punch machine in zombie mode to upgrade the Ballistic Knife into The Krause Refibrillator, and shoot at a downed ally to revive them with it from a distance.