"The Articulated Angstok (Tachyphytum multiplicatum) is a ceraintharoid organism capable of extremely rapid growth. The main body of the animal is generally buried, with only a small protuberance visible above ground. When it detects sound or movement, it will sprout into action, forming limbs and extensions to capture its prey. In a nutshell, it is the skeleton of a creature that is able to grow its bones. When the extensions reach the prey, a deadly mouth full of crooked spikes grabs the prey and crushes them to death slowly. Articulated angstoks grow in clusters, as illustrated by the old Trebhum saying “when you run from one Angstok, make sure you’re not running into a forest” (i.e. don’t focus so much on avoiding one problem that you end up creating more). Empty angstok husks, left behind after the organism has retreated back into the ground, are generally not dangerous."
Articulated Angstoks have predictable behavior. When you get close to their bone looking exoskeletons they will rapidly grow towards the Trebhum's leader. If it catches up it will grab the Trebhum in its jaws and crush it to death. However, if the Trebhum has the Aposematic Skin mutation the Articulated Angstok will let go. The Articulated Angstok can only grow so much before it cannot grow anymore and the hole in its exoskeleton will become closed.
If an Angstok has snatched one of your Trebhum, you can shoot water at its eyes (the back balls protruding from it) to make it let go of your Trebhum. The Toxic Trunk works even better.
Sometimes there will be chests with useful items hidden within the Articulated Angstok cluster.
There is a chance while the Articulated Angstok is chasing Trebhum to reveal a Rattle Seed instead of its jaws.