Does the Foe Glass Prove Snape = DD's Man?

[potioncat]

No: HPFGUIDX 155729

 
> Angie again:

> 
> All in all, I think the Foe Glass episode says more about the 
> unreliable nature of the Foe Glass (and perhaps all similar 
> magical "indicators"?) than whether Snape is truly DD's man.  If that 
> is the point, I wonder if the theme will rear its ugly head in Book 7?


Potioncat:
Hold on. It's the narrator that's unreliable, not the Foe Glass---oops 
wrong thread.

I can't get to canon, so I have some questions and impressions.

What was the context for Harry saying the Foe Glass wasn't reliable, or 
did he say Dark Detectors aren't reliable? And when he said that, was 
he correct?

Have we seen unreliable detectors? Seems to me everytime the Sneak-a-
Scope went off, there was a baddie around. Of course, everyone looked 
in the wrong direction. 

Crouch!Moody turned off one instrument because the castle was full of 
kids telling lies. (At least that's the reason he gave.) which would 
mean the instrument was a tad too sensitive.

When Harry looked at Crouch!Moody's Foe Glass--the very first time---C!
M distracted him away from it. I think he didn't want Harry to see who 
might show up. When a Foe Glass was showing figures during a DA class, 
Harry ignored it. Does anyone remember, was that the same lesson that 
Umbridge caught them? Seems like he should have paid more attention.

My point, (assuming I'm remembering this correctly) is that the 
Detectors are only as good as the wizard who reads it, but they in 
themselves aren't wrong.