The raging flood that takes Arlo's father. It's then brought back in flashback form when Arlo gets terrified by the storm. During the flashback, the flood suddenly gains a gaping, toothy maw, in which if you see it closely, it almost looked like a gigantic shark.
Poppa Henry: RUN, ARLO!
Thunderclap and his pterosaur cronies. At first, he and his group appear to be very goofy, but caring, trying to search for wounded survivors after the storm. But the more they talk, something seems quite off about them and a viewer will notice that their eyes are bloodshot, like they're crazed. And then Thunderclap swallows a cute animal alive and on-screen. He and his cronies fight over the dismembered remains of the critter - and then they figure out Spot is there and come after him.
A bit of Fridge Horror as the scene goes on - for most of the movie Thunderclap and the Stormchasers largely go after "critters" and small animals. It would be easy to assume that they only go after hurt and helpless animals, and only fight dinosaurs territorially like the raptors, until you realize that the very first thing Thunderclap said Arlo was asking whether or not he was injured - and once you know it's there, it's hard to miss the disappointment in his voice when he realizes Arlo isn't...
After Thunderclap subdues both his cronies, he lets out a defiant, half-laugh half-screech noise. It's... very unsettling.
When Arlo realizes they're trying to find Spot, he gives them the wrong direction, which fools two of them as they fly off. Arlo then turns around to find that Thunderclap stayed behind and is simply... staring at him. With those deranged eyes. Arlo is understandably creeped out and can't help but look towards where Spot really is, giving Thunderclap the reaction he was waiting for.
Their second appearance in the film has them emerge from the clouds, their mouths foreshadowing their arrival as if they're sharks in the sky. They succeed in capturing Spot the second time and fly off with him. When Spot manages to get away from them by wedging himself in a log, Thunderclap and his group start tearing apart the log to get at him, with Spot crying out in terror.
Shortly afterwards, Spot tears a huge hole in Thunderclap's wing membrane with his teeth, resulting in the pterosaur staring horrified at his damaged wing.
While fleeing from Thunderclap and his group the first time, Arlo notices a longneck dinosaur in the distance. He cries out for help, only for it to be revealed that the longneck is actually two Tyrannosaurs - Nash and Ramsey. Fortunately, they turn out to be good.
And when Arlo turns around to flee from the tyrannosaurs, Downpour strikes him down and the flock all begin to mob him. Thankfully, Nash and Ramsey chase away the pterosaurs before any real damage was done.
While searching for the long-horns, Arlo, Spot, and the T. rex ranchers come across the fly-ridden corpse of one along with a blue feather, a hint that the rustlers are actually raptors.
The raptors themselves. Unlike Thunderclap and his flock, they are simply territorial...but woe if you enter their territory.
Lurleane: Looks like (Arlo)'s trespassin'.
Bubbha: And what do we do with trespassers? Tell 'im, Earl.
(Arlo turns around to see Earl standing right behind him)
Earl: We KILL 'EM!
After Arlo manages to smack one of the raptors with his tail, the other says, with a crazed look in her eyes, "I'm gonna loveENDING YOU!"
The design of the raptors is also rather unsettling. They do have feathers, but unkempt and patchy, as if suffering from some kind of mange, while their teeth are awkward and gnarly and not the neat pointed teeth real-life raptors had.
That's to say nothing of, while trying to track the missing herd, it seems as though Spot had been leading them on a false trail. Butch proceeds to loom aggressively over Arlo, threatening to tear his leg off if it turns out he's been trying to dupe them. Thankfully, they notice the nearby carcass and feathers before he can act on this, but the threat was enough.
To some people (especially young children), the hallucination scene is this.
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