Hagrid seeing Thestrals

[earendil_fr]

No: HPFGUIDX 100077

There's a question I've been wondering about for a little while now. 
I didn't even try to use the archive search, I know I'm likely to 
spend hours on it (my dial-up modem will be the death of me) with no 
guarantee to find anything relevant.

Anyway, here we go:
We know from OotP that Hagrid can see Thestrals.
So whose death did he see? His father's maybe? Any other suggestion, 
anyone?

Or can Hagrid see Thestrals because he's a half Giant?
BTW, do we know if magical beasts (or even non magical ones) can see 
Thestrals?

Earendil.