Cold-Blooded

Cold-Blooded is a Tier 2 perk in Call of Duty: Modern Warfare 2 ' s multiplayer. It is unlocked at level 25. This perk removes the player's thermal silhouette when viewed by thermal optics, and makes players undetectable to all killstreak rewards. Players using Cold-Blooded will be invisible to the UAVs, Sentry Guns, Harriers and computer controlled Helicopters and simply will not be targeted (though players can still be killed by collateral damage from these sources). With Predator Missile, AC-130 and Chopper Gunners, players using this perk will still appear on the screen but they will not be highlighted by a red square, nor will the player's silhouette white. Thus, the best strategy during one of these kill streak attacks is to simply stop moving as the black and white resolution for such attacks is poor and moving objects are much easier to see.

Instead of appearing as bright white silhouettes through a Thermal Scope, Cold-Blooded players will appear as shades of gray similar to the environment. This may actually cause the player to be at a disadvantage on snow maps, as the gray has more contrast with the environment, whereas the white-hot silhouette of non-cold blooded players is much harder to spot against the white snow (of course, for this reason, most players choose not to use Thermal Scopes on winter maps, so the issue is often moot). As they are not truly invisible, moving Cold-Blooded players are much easier to spot through thermal scopes than stationary ones. As most Thermal Scope users are more accustomed to bright white blots on the map, it is easy to pass right over a Cold-Blood user.

The Pro version prevents the red name and crosshairs from appearing on an enemy's screen when they are looking at the user. It is unlocked by destroying forty enemy killstreak rewards (of any kind, even UAVs) while using this perk. If a silencer is added this is very helpful to sniper classes (though damage is reduced).

Tips

 * Cold-Blooded is extremely useful for anti-air classes, where it is usually used in conjunction with Scavenger and a Stinger.
 * With this perk it is not safe to stand next to someone without it during an enemy killstreak. They will be targeted and you may be killed with them when they are hit. However, in friendly fire games, you will be safer, as the average player will not attack players without red boxes since they will assume that you are friendly. Because of this, players trying to shoot down enemy aircraft with Cold Blooded should stand away from team-mates.
 * Some players prefer to use Cold-Blooded on knifing classes instead of the usual Lightweight, as stealth is an important part of survival.
 * Cold-Blooded is useful for Ninja Defusing as well. Since Cold-Blooded hides you from any form of detection besides direct enemy eyes, even if the enemy has called in a UAV recon, you will not show up on radar. Without Cold-Blooded, the bomb planter could spot you on the UAV while he is planting the bomb. If he were to catch this, he'd turn around and you would most likely be shot down. In addition to being hidden from radar, the Pro version of Cold-Blooded hides your name and red cross-hair if the enemy is looking at you, making it easy to hide in shadows around the map.
 * To get the Pro version of this perk more easily, in addition to titles and emblems associated with it, shoot at an Attack Helicopter, Pave Low, or Chopper Gunner which has already been destroyed by gunfire and is spinning out of control. Every bullet that hits counts as a destroyed enemy killstreak reward.
 * An effective strategy for destroying Chopper Gunners and Pave Lows is to have a Stinger with the Sleight of Hand and Cold-Blooded perks.

Trivia

 * The perk picture shows a lizard (a "cold-blooded" reptile) surrounded by snowflakes.
 * In reality, "Cold-Blooded" refers to an organism that cannot produce its own heat, referring to the fact that most of the weapons this perk blocks use body heat as a means of targeting.
 * There are three ways of obtaining the Pro version of this perk: shoot down enemy air support with a launcher, steal enemy care packages, or destroy enemy sentry guns.
 * There is a glitch which allows a player with this perk to collect points towards the challenges very easily. This requires the enemy to call in a Pave Low or Attack Helicopter. Once it has been destroyed shoot at it as it is falling out of the sky. For every bullet that hits it, it counts as 1 kill. It is quite possible to get 30-60 'kills' with an assault rifle or sub machine gun, or even up to 100 with a rapid firing light machine gun such as the M240, or MG4, towards the cold-blooded pro challenge this way for each helicopter. The helicopter has to be destroyed by bullets or by calling in an EMP, not a launcher such as the Stinger as it is completely blown up by these. However, the Harrier will not blow it up, so you can also destroy it with Harrier. A Silencer may want to be attached to hide your constant spraying from the enemy. Using an AT4 or RPG-7 to damage the Pave Low first can help reduce the number of bullets required to destroy the helicopter, since they do not destroy the helicopter in one shot.
 * Some players lie on the ground constantly switching your weapon. To other players, it will seem like you are a dead body, as although to you it looks like you are partially taking out your weapon, to others it looks like you have no weapon in your hand. With pro, even if an enemy moves his cursor over you he won't see your name and it won't light red, adding to the effect. This is especially useful in domination, as you can lie in a place that is completely in the open next to a flag and enemies won't shoot you.
 * If hold this perk and Ninja you'll be completely undetectable by any means other than direct sight.