LV, Nagini and Harry

[sridharj_ap]

No: HPFGUIDX 159060

Hi,

I was rereading OOP and was struck by a question I couldn't answer. 
A quick search here revealed some discussions which only increased 
my curiosity further, so I thought I would ask it anyway. Why is 
Harry able to "see" only when LV possesses Nagini? Otherwise, he is 
only able to feel LV's mood (again, only if it is intense).

Is it somehow related to the fact that Harry can understand 
Parseltongue? 

Another related question is if Nagini is a young Basilisk, but that 
somehow does not fit in. If Nagini is one, then biting Arthur should 
have killed him, since the bite was severe and there was a 
considerable time before Arthur was in St. Mungo's.

Any answers/theories/opinions?

Regards
Sridhar
P.S: I am wondering if this has been discussed and closed before. If 
so, kindly point me to the thread.