Application of lessons / Quirrell plot hole?

[pippin_999]

No: HPFGUIDX 45122

--- In HPforGrownups at y..., Barb P <psychic_serpent at y...> 
wrote:
>

> And, since one of Quirrell's specialties was supposed to be 
dealing with trolls (and Dumbledore knows this, as Quirrell 
contributed the troll to help guard the Stone), one has to wonder 
why Quirrell wasn't immediately suspect for letting the troll in, 
especially as he didn't do anything in particular to deal with it, as 
one would expect the resident troll-expert to do.  I can't 
remember whether this possible plot hole has been mentioned 
before...<<<<
>  

But he *was* immediately suspected, according to Quirrell:
**************
"Snape, who already suspected me, went straight to the third 
floor to head me off--"

PS/SS ch 17
***************
Snape suspects Quirrell, and has probably shared all his 
suspicions with Dumbledore. Suppose they even suspect that 
Voldemort is lurking inside Quirrell: what could they do about it?

 It isn't clear that anybody but Harry could have hurt Quirrell as 
long as Voldemort was inside him. Quirrell's not afraid of Snape, 
certainly, "Tried to frighten me,--as though he could when I had 
Lord Voldemort on my side,"  though Snape can do AK ("Give me 
a reason to do it and I swear I will") None of the high security 
precautions at Gringott's were able to stop Quirrell at all, and that 
was *before* he was possessed. 

Dumbledore's  hope, as I see it, was to lure Voldemort into 
looking into the Mirror, trapping him in front of it, or failing
that, to force another confrontation between Quirrell and Harry, 
but not until Harry had become strong enough to resist him. 
Thus the obstacles before  the Stone. 

Pippin