claimed animal companion

[Eltsac]

I'm new to this skills so I was wondering :

- What makes that a claimed animal will assist you in fight or not?
I have had a bear that was assisting me, but my stag was not.

- When I try to claim something I have two kinds of message :
When trying to claim a boar in Neverwinter's wood, I get "You can't claim that"
When trying to claim a wild stag in Neverwinter's wood, I get "You can't claim a wild stag" (with the name of the animal in the message)
What is the difference between both message? Two message means two different failures I guess ?
I would think that both the boar and the stag could be claimable. I'm level 50. Is it something about my 'animal empathy skill'? or about the animal's level ?
Help files are not really clear about that.

- if not yet it game, would it be possible to mount a mountable claimed animal?

El & co