Patronuses as Messengers

[Katie]

No: HPFGUIDX 177686

Re-reading GoF this morning, I noticed that when Harry brings DD down 
to the edge of the FF, after Krum and Crouch have been attacked, DD 
sends "something silvery and bird-like" out of the end of his wand up 
to the castle. He sent his Patronus, which we know was a phoenix, to 
alert the other professors at the castle. 

So, even though Harry didn't know what DD had done, and therfore, we 
didn't know, Patronuses *had* been used as messangers long before HBP. 

I just thought that was interesting, Katie