How did Umbridge know?

[theotokos]

No: HPFGUIDX 112858

In Ch. 22 "St. Mungo's Hospital for Magical Maladies and Injuries" Harry has just had the experience of being Nagini and seeing Mr. Weasley bitten.  The kids are now is DD office, Fawkes is keeping a "look out", and Phineas has gone to alert Sirius of the imminent arrival of the Weasley children and Harry.  In the American HB page 474:  
 
     There was a flash of flame in the very middle of the office, leaving behind a single golden feather that floated gently to the floor.
     "It is Fawkes's warning," said Dumbledore, catching the feather as it fell.  "She must know you're out of your beds....Minerva, go and head her off--tell her any story--"
 
I think it is agreed who the "she" is but how did she know?  It is the middle of the night for goodness sakes!  Does she somehow have the portraits watched or watching?
 
AND on page 470:  
     
     Dumbledore now swooped down upon one of the fragile silver instruments whose function Harry had never known, carried it over to his desk, sat down facing them again, and tapped it gently with the tip of his wand.  
     The instrument tinkled into life at once with rhythmic clinking noises.  Tiny puffs of pale green smoke issued from the minuscule silver tube at the top.  DD watched the smoke closely, his brow furrowed, and after a few seconds, the tiny puffs became a steady stream of smoke that thickened and coiled in the air....A serpent's head grew out of the end of it, opening its mouth wide.  Harry wondered whether the instrument was confirming his story:  He looked eagerly at DD for a sign that he was right, but DD did not look up.
     "Naturally, naturally," murmured DD apparently to himself, still observing the stream of smoke with the slightest sign of surprise.  "But in essence divided?"
     Harry could make neither head nor tail of this question.  The smoke serpent, however, split itself instantly into two snakes, both coiling and undulating in the dark air.  With a look of grim satisfaction DD gave the instrument another gentle tap with his wand:  The clinking noise slowed and died, and the smoke serpents grew faint, became a formless haze, and vanished.
 
What is that about?  It must be giving DD some sort of answers about Harry's vision.  Essence divided?  two snakes?  Does it have something to do with LV possession of Harry?
 
I am lost.
Theotokos




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