When researching sometimes I find it useful to just write my own summary of what I've just read in order to organise my thoughts so that I fully grasp the concept.
When we begin, growing in our mothers belly see are still very much a part of her. Even after we our born we are still in someways apart of her as we are unable to think of ourselves as separate and depend on her completely in every way. But then comes a time when we our able to view our self as separate we are the "subject" she is our first "object"(meaning thing that we know is not us) this is a very important time as is the beginning of our entire identity! Our sentience! And now when we are older when we encounter something that is not subject or object that falls in between it threatens this initial idea that allowed us our identity. This thing challenges our very first realization that we our a separate entity than everything around us. We have been able to know what is us and what is not us since the time we separated from our mother but now something threatens this and we our overcome with repulsive.