Originally named "Soulfire" Zombies because of their creation by replacing the heart of a victim (living or dead) with a touch of magical flame (producing greater animation and even a body temperature, allowing the zombies to infiltrate normal society), they quickly became known as "Bloody" Zombies, because of their tendency to explode in a graphic mess due to the animating flame heating up decomposition gases (in dead subjects) and bodily fluids (in fresher "volunteers") to the bursting point.
This problem was solved by a young anatomist turned Occultist who, in addition to retaining the flesh removed when the heart was replaced (an open chest wound that large tended to be a tip off to even the densest of monster hunters), removed the internal organs through an incision below the abdomen, and vented the upper torso with two punctures through the diaphram and into the lungs. Then, in a fit of ghoulish whimsy so prevalent in practitioners of the Occult, he carved out and replaced a symetric wound on the right side of the chest, and so were born the "Jack-O-Lantern" Zombies, or "Jack" Zombies for short. (They are also known - though mostly only by those individuals deviant enough to create them in the first place - as "Jolly" Zombies, both due to their increased activity and near normal temperature and coloration, as well as their need to vent excess heat by smiling, full grin, quite often. This later trait has made them almost as distinguishable to observant monster hunters as the open chest wounds of the "Soulfire" breed.)
While the magical hellfire that animates the Jack Zombies grants them greater mobility, a (near) normal body temperature, and even a degree of normal color, it does have one very distinguishing, yet also quite horrific, drawback. While in direct light Jack Zombies are almost indistinguishable from living humans (except for the scars of the "operation", which they take pains to hide), in anything less than near candlelight, the glow of the animating flame can be seen through the skin, as if the zombie were about to burst into flames. This glow is most prominant in the torso, even through single layers of clothing, but can also be seen in the extremities if not swamped by other light. In complete darkness, even the fingernails and hair of a Jack Zombie are lit with the unholy glow. (Some Jack Zombies are intelligent enough to make use of this effect, either as a daytime diguise or an extra touch of nighttime horror in the course of their other work.) When "killed", a Jack Zombie explodes in a cadaverous fireball, totally incinerating its old body, without doing any noticeable damage to it's surroundings. (A True Death will extinguish the animating flame, leaving the corpse exactly as at the time of the zombie's creation.)