Thanks for the chapter!
MC definitely does not have the faintest idea of common sense of the world as not only doesn't feel Parasite Monster a threat to be scared of, but already gleefully anticipating experience will get from defeating the parasitized monsters guarding it. Mana reaction is off. Or at least in LN it wasn't reaction was similar to that of bugs, but completely hid reaction within the barrier/mound. Gotta admit anyone not familiar with area might look past mound since it physically and magically hides the parasite monster, but anyone familiar with geology would find the size and shape of that mound to be suspicious, especially in a plain with no other big rock formations.
@Leo80221 Host could be but very unlikely. Considering the area the Host will be an enlarged and powerful version of one the plain's monsters. If parasite is bigger is better type on selecting a host it's probably one of the largest monsters of the area like a bull so no matter what else it ran into, the Host would be able to subdue it allowing Parasite to seize control and augment it like that Venom Snake MC killed. The Parasite itself is likely to be an insect like species or a larger form of a parasite on Earth as those are the ideal forms to sneak onto and perform parasitism on something else while a turtle would most likely not be able to stay attached to host much less sneak onto without being noticed and killed. Being a monster parasite it'll probably be bigger than a normal parasite, but could still be small enough to fit on an adult's hand and will have skills and/or magic as well.