Hola, buenas tardes.

Habrás visto (porqué no te lo cuentan casi ni en el TS) que hay gente que dispara de la ostia, que recarga a toda leche, que corre como un gamo, que tienen explosivos especiales, bazookas, etc ¿cómo lo hacen? con los PERKS del COD4 que no son más que una serie de características especiales con las que puedes configurar tu soldado para que sea más efectivo, más rápido, más mortifero, etc. Las características se pueden combinar y eso ya va según los gustos:

Sobre PERKS y funciones de cada uno:

Perk 1:

* Bomb Squad
Ability to seek out enemy explosives
* (2x) RPG-7
You will have an RPG-7 in the game.
* (3x) Special Grenades
You will be able to use special grenades in the game such as flash grenades.
* (2x) C4
When enabled, you will have two C4’s per spawn.
* (2x) Claymore
Trip activated exposive mines (Unlocked at Rank 23)
* Frag x 3
3 Frag Grenades (Unlocked at Rank 41)
* Bandolier
Adds more ammo to your clip (Unlocked at Rank 32)

Perk 2:

* Juggernaut
Gives you extra health.
* Sleight of Hand
You can reload your gun faster. (Unlocked at Rank 20)
* Stopping Power
Bullets do more damage.
* UV Radar Jammer
Jams Enemy Radar (Unlocked at Rank 11)
* Sonic Boom
Higher explosive damage
* Double Tap
Increased Rate of Fire. (Unlocked at Rank 29)
* Overkill
Carry two primary weapons, no pistol (Unlocked at Rank 38)

Perk 3:

* Extreme Conditioning
Allows you to sprint longer.
* Steady Aim
Increase hip-fire accuracy
* Last Stand
Pull out a pistol after you are downed to shoot your killer before you bleed out. (Unlocked at Rank 8 )
* Deep Impact
Increases penetration and damage of all weapons through walls or cover.
* Dead Silence
You make less noise as you move. (Unlocked at Rank 44)
* Iron Lung
Increases the time you can hold your breathe while zooming in with a sniper. (Unlocked at Rank 26)
* Eavesdrop
Allows you to listen in on enemy conversation within 30 meters (approximately 90 feet). (Unlocked at Rank 35)
* Martyrdom
Drop a grenade just before you die to kill any nearby enemies. (Unlocked at Rank 17)

por último te dejo un enlace a un vídeo http://www.vidaextra.com/2007/08/21-video-de-call-of-duty-4-sobre-el-uso-de-los-perks

Y varios ejemplos mas de PERKS: