The brain structure of a feral ghoul indicates that the regenerative ability of the neurological system that affords "normal" 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 Barrows. Despite the apparent lack of the higher reasoning they once had as humans, some are capable of semi-intelligible speech, as the Vault 34 security officers will occasionally growl out understandable phrases similar to the trogs of The Pitt, indicating that their vocal chords and their brain's speech centers are still relatively intact.
Dr. Banfield supports the theory that all ghouls will eventually become feral ghouls however, it should be noted that he has never taken the time to actually study a ghoul and is biased against them. It should also be noted that many of the ghouls in existence were born prior to the war and have yet to go feral making it quite possible that this theory is inaccurate.
As with normal ghouls, ferals are not only extremely resistant to radiation, they are actually healed by it, as can be seen when a glowing one uses its radiation blast nearby other ghouls. M.A.R.Go.T. also states that feral ghouls have no internal body heat.
Similar to ghouls, a crazy ghoul's body has been severely ravaged by necrosis, and as such they look like nothing more than shambling corpses. Differentiating them from normal ghouls, though, is the equally ravaged mind of ghoul crazy; they have long since lost their sense of reason or higher thought and as such follow basic animal instinct.
As ghoul crazies have long since lost their ability to reason they have relatively underdeveloped tactics when in combat. They simply shuffle towards their closest enemy, thus fear is unneeded when engaging in combat with isolated individuals. Crazy ghouls often travel in groups, though, and as such can pose a threat when greatly outnumbering their foes. As fighters they are meager at best.
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Glow crazies are simply glowing ones who have gone mad, just like any other feral ghoul. The main difference is that they have become bioluminescent from all of the radiation they have absorbed over the years.