As ISIS empties a barbaric playbook of chemical attacks, child suicide bombers, and human shields in a desperate attempt to hold onto Mosul, it may also be adding cannibalism to this poisonous script.

The root of the Islamic State's maniacal desperation stems from a tightening noose being pulled on by Iraq military forces as they attempt to wrest control of the northwestern Iraqi city.

In an offensive begun last October, the five-month-long battle has turned the once entrenched citadel of ISIS control into a modern-day version of Stalingrad, with two highly armed opponents engaged in fierce, bloody street fighting.

ISIS appears to be playing the role of the German army as the U.S.-backed Iraqi troops have dealt a series of devastating blows, leaving a remnant of 2,000 unyielding Islamic State fighters, along with several hundred foreign jihadist allies, holed up in the western half of the city.  With its caliphate metropolis on the verge of collapse, it's all hands on deck for the sociopathic Islamists, leading them to take any and all brutal measures to desperately stave off defeat.

To that end, ISIS militants have deployed child suicide bombers as part of their battle plan, a youth-centric stratagem that has left more than three hundred ISIS "Cubs of the Caliphate" killed to date.  Unlike Japanese kamakazi pilots plied with sake to garner the courage to undertake their lethal missions, ISIS uses a nonalcoholic method to instill its young wards with suicidal fortitude, relying instead on promises from Allah of a great heavenly reward.

To be fair, ISIS isn't alone in using children in such a grotesque manner, given the longstanding practice of Islamist terror groups around the world to utilize underage suicide bombers, including those with Down syndrome, making children the Islamists' favorite choice of human explosive.

Unfortunately for ISIS, exploding children hasn't been enough to turn the tide of battle, so naturally, its agents upped the ante by employing human shields picked from among the nearly 750,000 Iraqis trapped with them to halt the Iraqi advance.  Those who resist the urge to be used as human armor are eagerly gunned down by ISIS fighters, a chilling fact that still hasn't prevented nearly 50,000 civilians from fleeing their captors in the last several weeks.

Not to be deterred, ISIS took the next logical step and launched rockets reportedly containing mustard gas against civilians residing in Iraqi-held eastern neighborhoods.  International outrage aside, it was a routine deployment of barbarism for ISIS, given that the group has been suspected of using chemical weapons dozens of times since 2014, including a 2016 rocket-launched chemical attack against American soldiers stationed at the Qayyarah air base near Mosul.

Outside its attempts to turn Mosul into a World War I-style poisonous gas-filled battlefield, it should be noted that ISIS tactics differ little from the global myriad of jihadi-crazed terror groups.  From Boko Haram to Al Shabaab to al-Qaeda to the Taliban and other mutant fanatical outfits, they all use a similar standardized version of Islamist monstrosity.

Yet the decades-long litany of unrelenting atrocities undertaken by these organizations led many in the world to grow numb to their effects, opening the door for ISIS to burst onto the scene and captivate imaginations with new levels of barbarity, like a movie producer who offered added shock value to an Islamist horror genre grown stale.  ISIS fit into this role neatly, given its self-identity as Islam's really true believers, avid acceptors of a literal translation of the Koran who view many of their fellow Sunni Muslims, let alone the blasphemous Shiites, as less than pure followers of Allah.

That's why, in its zealous mission to create a 7th-century Islamic caliphate, ISIS separated itself from the other Islamist terror packs by creating its own unique brand.  This included creating such fine tag distinctions as drowning people in cages, dunking people in vats of nitric acid and scalding tar, grinding bodies into meat, burning people alive, and crucifixion.  It should be noted that while ISIS is a committed equal-opportunity anti-apostasy enforcer, targeting fellow Muslims and even its own fighters not fully on board with its medieval agenda, it has reserved most of these heinous punishments for Christians and other religious minorities.

Like any good marketer, ISIS also became adept at using social networking sites to share through video and photographic uploads its jihadi product line of mass killings and executions.

While other Islamist terror groups employed similar media tactics, ISIS efforts have gained better traction, given the more gruesome material it had to offer – in particular, a signature twist of using children as a main subject feature in its promotional catalog of torture and death.

ISIS also offered a more enhanced benefit package to gain better applicants in a crowded jihadi job market by establishing a fully functioning sex slavery system comprising young women and girls, some as young as nine, from Christian and other non-Muslim groups.  Given Islamic taboos against premarital sex and a deeply rooted Islamic attachment to prepubescent girls, offering these children up for systematic rape multiple times a day proved to be a great recruiting tool to entice sex-starved ISIS fighters.

While all these ISIS innovations had the benefit of instilling a lethal dose of fear into anyone who had the misfortune to fall under the organization's territorial control, they also produced detractors among the group's jihadi competitors.

An example of that professional dismissal was found in documents taken from Osama bin Laden's Pakistani compound, which detailed complaints that ISIS savagery was damaging al-Qaeda's jihadi reputation, which admittedly is akin to Jeffery Dahmer being offended by the excesses of Hannibal Lector and the latter's potential negative impact on the serial killer community.

Nevertheless, given the ruthless ISIS reputation, it does make one wonder how far ISIS can sink into the slime in its efforts to keep from losing Mosul, a question that may have been recently answered in an instructional handbook taken from one of the jihadi training schools that pepper the ISIS caliphate.  There, a curriculum lesson on how to eat non-Muslims if food supplies run dangerously low was outlined, along with precise instructions on how to prepare a properly cooked human.

The ISIS cannibalism guide gives Koranic justification for consuming non-Muslims, an academic lesson the mentally unhinged Islamists have apparently passed, given their already documented serving of human food, albeit to a welcoming invitee.  That truly horrifying and despicably insane act was committed near Mosul against a Yazidi woman who was starved for several days and then fed the remains of her three-year-old son.  She was told by her deranged captors that it was meat mixed with rice.

In a bit of bad news for ISIS, though, the scarcity of Christians and Yazidis still alive in Mosul due to its genocidal acts means that the jihadis may be forced to go against Koranic strictures and substitute fellow Muslims on the entrée plate.  Even though that gruesome possibility remains on the table, not everyone is waiting to join in, as Islamic State leader Abu Bakr al-Baghdadi and some of his aides have reportedly fled Mosul to parts unknown.

While, if true, that news may signal the end of the living nightmare that has plagued the people of Mosul, given the inexhaustible cruelty of the Islamic State, the nightmare will continue to play out in what remains of its dying caliphate.

Frank Crimi is the author of Divine Roosters & Angry Clowns. He can be reached at frankcrimi@politicallyunbalanced.com.