If Higurashi's taught me anything, it's that the power of friendship can drive away any mind-altering parasite. Yuki should give that a shot. I bet it'd work.
It feels, with his colleague awol with the “old-man” parasite, the scientist is becoming more and more disillusioned with the entire mess. He sounds cold, but this is his way of giving Yuki a push, regardless of what she decides.
Its kind of sad that I was genuinely surprised by the scientists bothering enough to clean up the corpse. Fucks up the study if everyone in town starts getting sick from a pathogen source they can't even perceive, I suppose.....
Maybe they can figure something out from the body. If theyd actually do anything USEFUL with that...... eehhhhh.
I do like his advice, though. He's right. if she doesn't decide now, it'll be agony every time she so much as sees someone affected....