[Etara]

I already messed this portion up once so want to make sure I understand this completely. I think I may have given an enchanted rat to a healthy rat and that cause the fail, but this I do not understand which is the Research Briefing given to study:

1. (First Photo) In the research book, why does the 0 turn to an x on the next page? I would think it would remain being a healthy rat, no? Screenshot below: