An Argentinosaurus herd is peacefully grazing on their nesting grounds when one of them gets bitten by a horrifying-looking, zombie-like hadrosaur. Soon, the bitten dinosaur starts showing similar, zombie-like symptoms to the hadrosaur, and eventually turns into a rampaging monster, slaughtering its entire herd and their nests. Spear and Fang chance upon the massacred dinosaurs, and get chased down by the infected monster. They spend the night in a cave hiding from the monster, where Spear has a nightmare of getting infected himself. After the duo leaves the cave, they get attacked again by the monster, who eventually follows them into a volcano and falls into lava from its weight. The episode ends with Spear and Fang somberly watching the creature burning to death.
This episode features the following tropes:
- Alas, Poor Villain: The plague monster's death is a somber moment. It was trying to kill Fang and Spear the entire episode but it never wanted to become a monster.
- Artistic License – Paleontology: The sauropods are shown chewing their food (in real sauropods the chewing was actually done inside the stomach by rocks they swallowed), and are also able to gallop, which would be impossible for such a large animal.
- Ax-Crazy: The plague monster attacks everything in sight, starting by killing its own herd.
- Body Horror:
- After becoming infected, the sauropod ends up becoming more and more like a rotting corpse and later on, when it falls into lava, its flesh becomes horribly burnt red. Several cuts after it rips open sufficient tears in its own skin and muscle shows there's nothing left inside its body aside from its skeleton, just a black void.
- The infected hadrosaur as well, with most of its spine showing through its back as its flesh rots off.
- Spear's Nightmare Sequence shows that he's particularly horrified by this aspect of the disease, watching the flesh slough off his and Fang's bones in the same manner after the monster bites them.
- Book Ends: The song that was playing at the beginning of the episode (called Tragic Death) is heard again near the end when the infected Argentinosaurus meets its brutal demise by being disintegrated in lava, cementing the experience that its death was not meant to be cathartic nor triumphant, but a heartwrenching one.
- The Chase: The entire episode is about Spear and Fang trying to escape the plague-ridden beast, as fighting it could result in them getting infected.
- Convection, Schmonvection: Spear and Fang end up in a volcanic field and are able to navigate it even though the floor itself should've been too hot to even cross. It's only making contact with the lava itself that seems to have any effect.
- Convenient Weakness Placement: Spear and Fang happen to come across a volcanic field after crossing the ravine, where the lava turns out to be the only thing capable of killing the plague monster.
- Diabolus ex Nihilo: The virus that turned the Argentinosaurus into a monster. Where did it come from? Is it a naturally occurring virus or could it possibly have a supernatural origin? Could there still be more infected creatures out there? We’re never told anything one way or another.
- Enemy Rising Behind: The plagued Argentinosaurus makes its presence known to Spear and Fang by slowly rising up behind them from a prone position.
- Evil Smells Bad: The scent the plague monster leaves on the dead Argentinosaurus herd members repulses Fang. Notably it also does not attract flies, which were seen earlier around the posteriors of the Argentinosaurus.
- Expy: Of the Rage virus from 28 Days Later. The symptoms are functionally identical, from the unbelievably bloodshot eyes to the vomiting blood.
- Gentle Giant Sauropod: Initially played straight with the Argentinosaurus herd peacefully grazing in the valley. Then gets horrifyingly averted by the infected Argentinosaurus, who becomes an Ax-Crazy, destructive monster.
- Gross-Up Close-Up: While Spear and Fang sneak past the infected Argentinosaurus, we get to see a close-up of the thing's flesh melting/rotting off its sickly-green sore-covered body, accompanied with disgusting noises. It gets even worse when it falls into lava and its flesh starts to burn.
- Implacable Man: The plague monster will stop at nothing to pursue its target, even ripping apart its own body.
- Instant Illness: It takes a few seconds for the Argentinosaurus to start showing signs of infection after being bitten by the infected hadrosaur. Depending on how long the cut is suppose to last, it could have fallen to madness by the next day, or even within hours.
- The Juggernaut: The plague monster is all but unstoppable. It smashes through any trees in its path like they aren't even there. When caught in a canyon, pulling itself free does more damage to its own body than Spear and Fang could have ever done. It takes repeated exposure to lava before it finally goes down, and that's due to a combination of its weight and its legs burning away keeping it from getting out in time.
- Kaiju: The plague turns the normally peaceful Gentle Giant Sauropod into a zombified rampaging monster that will relentlessly pursue and brutally slaughter every living creature it sees.
- Late-Arrival Spoiler: Months before the previous episode aired, this one was shown on April Fool's Day and showed Fang alive and well.
- Lava Is Boiling Kool-Aid: Not only can Spear and Fang easily walk next to pools of lava and only mildly get hurt when it splatters on them, but the plague monster sinks into it as if it was in a pool of mud. In real life something would have to be denser than rock to sink in lava, since it literally is rock.
- Lightning Bruiser: The plague monster is just as strong as you would expect a creature of its size, and is much faster than any dinosaur its size should be.
- Logical Weakness: The plague monster's size and weight do it no favors when it tries to chase Spear and Fang down a ravine, gets it temporarily stuck when it tries to get through the narrow exit, and ultimately does it in when it jumps towards the duo but cracks the fragile lava rock and sinks into lava a second time.
- A Molten Date with Death: How the plague monster meets its end, although it takes being submerged in lava twice before it finally dies and turns to ash in the wind, and the second time only sticks because it fell in long enough for its legs to burn away and thus prevent it from getting out again.
- Nightmare Sequence: Spear gets one, where he and Fang get bitten by the infected dinosaur and turn into plague monsters themselves.
- Oh, Crap!: Spear and Fang's reaction to the plague monster throughout the episode, starting as soon as they come upon the dead herd. Spear has it immediately, and Fang joins after a quick smell of the corpses.
- O.O.C. Is Serious Business: Spear is a brave caveman who normally charges into battle with animals many time his size. He's absolutely terrified of the plague monster and spends almost the entire episode in fear from it. Fang is the same way, doing an instant about-face after scenting the monster's traces on the Argentinosaurus corpses, and is unwilling to approach it even when it seems unconscious or dead after falling off a cliff.
- Outside-Context Problem: The infected beasts are this. While previous threats were at least plausible for a fantastical prehistoria setting, the infection is almost supernatural and otherworldly by comparison.
- Red Eyes, Take Warning: Inverted. The Argentinosaurus already have red eyes, it's when one gains the yellow veins in its eyes that the Hadrosaur had that it falls to madness. Notably the Hadrosaur's eyes go pure red only when it dies and is at peace.
- Riddle for the Ages: What in God's name is the Plague of Madness? Where it came from and why it has the effects it does are never addressed. For Spear and Fang, the only thing important about the plague is getting away from it.
- Run or Die: Neither Spear nor Fang can do anything against this monster, other than running away from it and/or trying to sneak past it.
- Scenery Dissonance: The attack of the infected Parasaurolophus and the first crazed rampages of the infected Argentinosaurus both happen in the middle of what appeared to be a peaceful and sunny day.
- Shout-Out: Both the infected Argentinosaurus vomiting a stream of blood into the lake and several shots from above at an angle, roaring with it's mouth open, very much echo similiar moments in Shin Godzilla.
- Shown Their Work: The sauropods have the correct forefoot shape, with only one claw.
- Stunned Silence:
- Fang and Spear don't bat an eye when they see a single dead Argentinosaurus but when they see that the entire herd had been slaughtered yet left uneaten, both are left gazing silently once they see the full extent of the carnage.
- As the Mad Sauropod burns after getting trapped in the volcanic geyser due to its size and weight, Spear and Fang watch in morbid fascination as the beast refuses to die. But their horror soon turns to sadness and pity as they feel bad for the creature as it finally perishes and becomes ash in the wind.
- Super-Persistent Predator: The infected Argentinosaurus attacks everything in sight without any self-preservation instinct. It runs into a volcano completely ignoring the lava and even survives being submerged in it the first time.
- Notably averted with the Hadrosaur, which runs around aimlessly screaming and only bites the Argentinosaurus when it ends up running into it.
- Technically-Living Zombie:
- The infected dinosaurs do not actually die from the plague, but they turn into zombie-like monsters with green, rotting flesh and red eyes. In fact, none of the Argentinosaurus that were clearly bitten and killed by the infected one rose back up as zombies, meaning that the plague only affects those that are still alive.
- The Hadrosaur, possibly in the later stages of infection, is far more mindless and wild than the Argentinosaurus and only attacks it upon happening to make contact with the larger beast. The disease seems to have rotted away its ability to even focus on prey.
- Tragic Monster: The infected Argentinosaurus may be terrifying, but it is merely the victim of circumstances beyond its control. Before the disease fully takes control, it is in obvious agony. When Spear and Fang finally kill it, they do not celebrate; they only watch, clearly saddened, as it dies.
- The Virus: What has infected the dinosaurs is never explained and the viewer is shown no evidence or hints of where the disease came from nor the patient zero of the whole mess, however, whatever the disease is, it turns anything infected into rage filled monsters that will attack any nearby creature while allowing it to ignore pain or fear.
- Vomit Indiscretion Shot: After being bitten, the Argentinosaurus is overwhelmed with thirst and tries to drink it away. It then vomits a massive amount of blood into the lake, much to the dismay of the other sauropods.
- Would Hurt a Child: The plague monster tramples all the Argentinosaurus eggs, presumably including its very own offspring, and slaughters the juveniles in the herd along with the adults.
