A Pronoun Problem

A Pronoun Problem

The passage below comes from a book, Molecular Biology Of Ecology.
https://books.google.co.kr/books?id=_qftSZeUeB0C&pg=PA316&dq=%22When+one+individual+attacks+another%22&hl=en&sa=X&ved=0CBoQ6AEwAGoVChMIy-fj-b6lyAIVAmOmCh1J8AsQ#v=onepage&q=%22When%20one%20individual%20attacks%20another%22&f=false

Any social interaction other than mutual display can be dissected into a series of behavioral acts by one individual (the donor of the behavior) directed toward the other (the recipient). One individual delivers food, the other receives it; one threatens, the other is threatened. When one individual attacks another, ?it may be thought of as the donor of a behavior. The attacked individual usually responds by standing ?its ground or by fleeing; in either case, ?it becomes the donor of a behavior.

I'd like to ask what the three underlined 'it' stand for.

I have my answers.
?it : one individual (the attacker and donor)
(Am I right?)

?it : the attacked (the recipient)
(Am I right?)

?it : ?

It's number ? that makes me post this thread. It seems to refer to the attacker and donor in the sense of context.

But 'in either case' prevents me from drawing a conclusion.

'In either case' seems to mean 'whether it stands it's ground or flees'.
(Am I right?)

In that case how '?it' also seems to refer to 'the attacked'.
(Am I right?)

Then how does the attacked, which is supposed to be the recipient, becomes the donor of a behavior, as in the last sentence?

Let me out of this deadlock.

Regards.