The first sign of osietic corruption is excessive bloodlust—serpies are by nature a species that requires to feed on blood due to a need to balance out their lack of memoria. They don't produce as much memoria as humans do, and since memoria tends to be tangible in the bloodstream, serpies feed on blood to obtain memoria. Corrupted serpies will have a heightened need for blood, memoria, and osietic energy combined.
Some serpies are able to hide their increased bloodthirst by abiding irregular feeding patterns, such as feeding past midnight or in the dark when others rest, but overall, if you pay just about enough attention to when a serpie goes out to hunt, you may be able to tell whether they have a chance of being corrupted or not.
Another sign that a serpie is possibly corrupted is unnatural glowing. All serpies have a faint glow to them when they swim underwater at night. It's not a vibrant glow normally, and it doesn't tend to have strong colors. Usually, a serpie's glow will have shades of pale blues or emerald shades and maybe even a pastel pink, but it's likely to be a muted shade of it. Colors such as aquamarine and other intense colors like scarlet are more common in corrupted serpies.
The glowing is usually just to attract attention, but most of the species don't pay nearly as much attention to it as humans do—in fact, it's usually only humans and other species who take note of it instead of the serpies themselves.
Another sign that goes with increased bloodthirst is sharper canines and fangs. Serpies have naturally sharp teeth to help dig into the flesh and create wounds for their prey, but these teeth even sharper and slightly curved, so as to create a wound both when the tooth enters the flesh and leaves it. Serpies also may contaminate their prey with osietic energy if they have an excess of osietic energy, causing the pray to experience numerous adverse effects, all of which tend to be unpleasant, ranging from mild headaches to nausea all the way temporary immobilization in some extreme cases.
The last sign and likely the most obvious sign of osietic corruption is when a serpie either has slit pupils or empty eyes. When a serpie is at its last phases of osietic corruption, its pupils will turn into slits. If the osietic corruption is not detained by then, the eyes will become blank or empty, so to speak. These eyes see better in the dark, but they also require osietic energy to remain functioning. The only other thing that can keep a corrupted serpie alive is excessive amounts of memoria, which is also linked to the excessive bloodlust.
The last phase of osietic corruption is when the sclera of the eyes becomes blackened and the irises receive their color, glowing in the dark. This is a sign of the last stage of osietic corruption, and saving someone from the corruption at that stage is typically impossible due to the high levels of osietic energy in the bloodstream.
It's important to maintain distance from corrupted serpies not just because of the threat they pose when they become bloodthirsty and aggressive, but because if they taint their prey with osietic energy, the corruption could spread to their prey too. Corrupted serpies will likely isolate themselves from others who aren't corrupted by a fear of being murdered by their purified kin and by fear of being ostracized.
Thankfully, osietic energy is more restricted to the public, and the more pure forms of osietic energy is now under the direct management of only the family that rules over Sergrela—Niam's family. The location of where they extract the osietic energy from is a secret as of now, and considering past incidents, it's likely they'll keep it that way.
A last note of osietic energy is that besides all of the risks it brings and its uses for serpies, there are other two uses for it—one of them is for humans and other species. To other species, osietic energy cannot be wielded outside of Sergrela because its properties are only in play within the cold waters of that region.

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The Fractured Mirror of Phasmophobia ╱ apply fiction
Fantasy「 どこまでも このうたの おもいでは 消えない 」 ? ?emoria. ─────────── Out there lies a mirror with a world inside it. Beautiful, bewitching .. not all can look within it. Care to take your chances and peer in its depths? category ; apply-fiction...
THE SERPIES
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