Some questions on my mind

How did the first woman who was infected by the rat know she was part of a hive mind? Why did she choose to and how did she know how to infect someone else? Is there some core need for infected to infect others?

If so, they’re not only trying to infect Carol and the others because it’s so great to be one but because they’re programmed to.

I wonder if they want to archive something in particular that requires a certain amount of people.

The hive mind seems to lack the ability for critical thought so they might be oblivious to the programming if building towards something feels inherently rewarding for them.

Bonus question that probably won’t ever be answered: is the human hive mind compatible with an alien hive mind?