Floo/head-in-the-fireplace & Hogwarts defenses

[abigailnus]

No: HPFGUIDX 57559

<snip summary of information on Floo travel/communication>

Amanda has deduced, correctly in my opinion, that Floo powder is used for purposes of 
communication and travel.  However, this discussion, if I'm not mistaken, started with a 
question about Hogwarts defenses - if Hogwarts is so impregnable, how is it possible 
that its Floo fireplaces are connected to the outside world?

The obvious answer is that Hogwarts has a firewall - communication with the outside 
world is possible, but not transportation to or from it.  However, in the very first Floo 
communication scene in GoF Molly is able to place a piece of toast in Amos Diggory's 
mouth.  This suggests that, at some level, Floo communication is Floo travel - a certain 
part of Amos Diggory's body was present at the Burrow, able to take an object with it.

I suppose it is possible that Hogwarts grates will allow this limited contact with the 
outside world, as it is hard to imagine that a disembodied head could do a great deal of 
damage, but surely the applications of Floo communication for the purpose of spying 
can't have escaped the notice of whoever it was that designed the castle's defenses?

I've had the sneaking suspicion for a while now that the defenses on Hogwarts are more 
psychological than physical - everyone knows that the castle is impregnable, so no one 
tries to get in.  Dumbledore's presence probably helps, too, but really, the castle is 
protected by ancient and outdated spells which no one has bothered to upgrade or 
update in centuries.  It must be obvious by now that we will see someone apparate in or 
out of the castle, the prohibition has been stated too many times, but now I suspect that 
Hogwarts may be breached in other ways.

Abigail