My three questions

[Ersatz Harry]

No: HPFGUIDX 56800

Having recently finished GoF, I have the following three questions,
though the second really pertains to SS.

(1) Why was Dumbledore seemingly unable to detect Crouch as Moody? 
You'd think old Albus would have some devices or powers for this sort
of thing, but he seems only human... er, Muggle... in this instance. 
Back in SS, he also was seemingly unable to detect the presence of
Voldemort on Quirrell's head, and you'd think that someone would pick
that up, which leads me to the next question.

(2) Assuming that Voldemort became a permanent part of Quirrell at
some point, at least until the end of SS, why did Harry's scar not
hurt *every* time that Quirrell/Voldemort was nearby?  Yes, there are
instances where the scar hurts inexplicably (to Harry), but I don't
get the impression that it always hurt in Quirrell's presence later in
the book, and you wouldn't think that Quirrell would have to be that
far away for the effect to work.

(3) Coming back to GoF, why did Krum catch the snitch at the World
Quidditch Cup?  Ron's explanation at the time (that Krum saw the game
as hopeless and wanted to end it his way) did not feel convincing at
the time, and I fully expected another explanation to emerge during
the course of the book.  None did.  Further, can we possibly believe
that Fred and George Weasley made their absurd bet with Bagman without
some prior knowledge about the outcome?  Certainly they wouldn't have
wanted to throw away their money.

Ersatz Harry

PS Another fun anagram: Bartemius Crouch = Cruciatus Hombre