Feral ghoul

Feral ghouls, mindless ghouls, ghoul crazies, feral necrotic post-humans or zombies are ghouls (humans mutated by radiation) that lost their ability to reason and have become aggressive animals. They react mostly on instinct, making them very similar to fictional zombies. Indeed, this similarity has caused much discrimination towards the ghouls that have retained their mental faculties.

Biology
The brain structure of a feral ghoul indicates that the regenerative ability of the neurological systems that affords typical necrotic post-humans their longevity does not extend into the higher reasoning functions of the brain itself. This condition is referred to as "ferocious post-necrotic dystrophy", according to the ghoul physician Doctor Barrows.

As the reasoning and high order thinking portions of the brain deteriorate, the ghoul subject becomes increasingly hostile, giving into a carnal need to feed as opposed to the capacity for thinking and reasoning that a non-feral ghoul retains. It remains unclear exactly what precipitates this change in biology and psychology, but anecdotal evidence seems to indicate that non-social ghouls, or those in isolation, are more prone to the condition.

It is also quite possible that this is a gradual process, meaning that eventually all ghouls would succumb to this condition. However considering the existence of ghouls that have been born prior to the war, it is quite possible that this theory is bunk, or that the rate of degeneration is dependent on the individual and surrounding factors.

Behavior
Feral Ghouls often cluster together in dark, cool environments, like sub-basement-level or totally underground areas, only occasionally leaving their hunting grounds into open air. However, the myth that ferals fear light is false. Occasionally, the player may encounter one or two ferals out in the open. Isabella Proud's research seems to confirm that ferals do not fear or avoid the light.

Frequently, Ferals will wander from place to place, stopping at fallen prey to feed, but will immediately attack any and all non-Ghoul creatures they come across. Upon detecting a non-Ghoul, most Ferals will make a high-pitched gurgle or screech, and set to search the area. Upon sighting prey, they will often scream once more, alerting any nearby Ghouls, and attack.

One interesting note with Ferals is that they seem to be fooled with rudimentary means. The Ghoul Mask, seemingly nothing more than the hollowed-out head of a Ghoul or several pieces of a human head stitched together, still seems to deter Ferals from attacking. When wearing the Ghoul mask (or using a stealth boy) the player can observe relaxed ghouls actions- Including twitching, bending down, having fits or sniffing the air. If wearing the ghoul mask, Ferals will often turn their head to the side and stretch their necks when you come near them, as if they are confused.

Note that Roy Phillips(Quest: Tenpenny Tower) told you that if you get close to the Ghouls they will "sniff" you out and attack you if you have the mask on. This is untrue, for it is a fact that they cannot smell due to not having noses.

Controversy
Whether this suggests that Ferals only track through sight, or that their other senses have become dull enough not to recognize prey through movement or scent is unclear, but would explain why Ferals do not attack other, sentient, Ghouls. Their sense of smell will still serve them, but only at a very short range.

What should be of note to the player, regarding what was said above, is that Feral Ghouls are Ghouls that have simply gone crazy. Ghouls were once humans. The reason there are so many in the metro tunnels around D.C. is that after the bombs fell many citizens sought refuge in the tunnels( hence the multitude of desks, beds etc).

It can be concluded Ghouls hunt primarily by sight and sound, like all other creatures in Fallout 3. They don't hunt using other senses because they are human derived creatures. Because of this, the ghoul mask fools them because they see a "Ghoul" and do not (or cannot) use smell to identify them.

Feral Ghoul
Feral Ghouls are the basic feral ghoul variant in Fallout 3; naked and noticeably weaker than standard human opponents, they are easily dispatched with one or two headshots from any decent weapon or a solid hit from a decent melee or unarmed weapon.

Feral Ghoul Roamer
Feral Ghoul Roamers wear what appears to be the remains of combat armor, and are somewhat tougher than standard Feral Ghouls, being roughly on par with mid-level human opponents in terms of durability (i.e. requiring about 3 or so hunting rifle headshots to kill). It is possible that Roamers are ghoulified U.S. soldiers as they wear tattered remains of Combat Armor.

Glowing One
Glowing Ones are the rarest of the Feral Ghouls; they have even higher durability than Feral Ghoul Roamers, and can take several hunting rifle headshots before expiring. Additionally, they periodically emit a 360 degree pulse of radiation that damages human enemies and heals any nearby Ghouls.

Feral Ghoul Reaver
Feral Ghoul Reavers appear in the Fallout 3 add-ons Broken Steel and Point Lookout. They are much more combat-worthy than other ghouls, and have the ability to throw irradiated chunks of goo. Aside from the damage they can inflict, Reavers also have great endurance and boast one of the highest HPs in the game, being able to survive even attacks from the Fatman.

Swamp Ghoul
Swamp Ghouls inhabit the swamps of Point Lookout. Aside from their paler coloration, they are very similar to standard feral ghouls in both general appearance and combat abilities.

Endless Walkers
Endless Walk is the punishment in which a ghoul from the Reservation is stripped of every worldly possession, including clothing, and sent marching into the wasteland. No ghoul has ever come back from the Endless Walk (exiled from the Reservation Otto Stead was saved by governor Dodge at Hoover Dam). Another source of Endless Walkers in the Boulder area is the Crater, the remains of NORAD.

Not all Endless Walkers end up scorpion food, at least not at first. On those rare occasions when one survives more than one year in the wasteland, they turn into wandering, voracious creatures on an endless quest for flesh. Due to their prolonged, open exposure to the desert sun, high radiation, and other hardships of the wasteland, these unfortunate ghouls, who were banished naked from the Reservation, look like walking, sun bleached chunks of beef jerky. Their constant exposure to the hot sun and high levels of radiation has caused their skin to toughen into natural, hardened leather, but at the same time, their brain has completely cooked.

Appearances
Feral ghouls appear in Fallout (in random encounters, as "mindless ghouls"), Fallout 2 (as "ghoul crazies") and Fallout 3 (where they are actually named "feral ghouls" for the first time).