[Eryops]

Originally Posted by Joly

Spoiler for Rika, the manga, Hinamizawa Syndrome:

The manga shows Rika scratching her throat out after the injection and after stabbing her throat out. I'm not sure how she had the strength to do that... o_o or is some of that apart of Shion's hallucinations?

Just ignore the manga. After all it also shows Rika meeting Bernkastel, which never happened in the VN, so I'd take everything in it with a grain of salt.

Originally Posted by Dante of the Inferno

Spoiler for Counter-discussion:

Onisarashi-hen, though similar to the other arcs in that it fosters intense delusions, is the major exception to the entire series. The feelings and situations created were the direct result of mental instability, since she had never been to Hinamizawa, the only place where the parasites are found. Since the parasites cannot (as far as we know) spread from person to person, Hinamizawa Syndrome cannot explain her behavior. Furthermore, there is not a single mention/depiction in Onisarashi-hen where she displays physical symptoms (i.e. throat scratching). The arc played more toward the "demon blood" explanation, pointing to perhaps a genetic issue and not an environmental one. The entire arc should not be considered in any explanation relating to Hinamizawa syndrome.

She visites Hinamizawa in Matsuri. Even if you ignore that, there's no reason to think she never visited her relatives in Hinamizawa as a child considering that she lived so close to the village.