"in essence divided?" from OOTP chapter 22

[nicouise]

No: HPFGUIDX 120698


I apologise if this has been posted before but I could not find any 
history of it on the site and am a first time poster so please be 
gentle!!!!.  I am re-reading OOTP as I am sure we all are in 
preparation for HBP and I am curious about the instrument which DD 
used in his office after HP had his dream of AW being attacked in 
the above named chapter. 

It is described as a fragile silver instrument and when DD tapped it 
with his wand it issued tiny puffs of pale smoke which then 
thickened into a serpent's head.  DD murmured "naturally, naturally" 
to the serpent and then "in essence divided?" after which the 
serpent spilt into two snakes, "coiling and undulating in the dark 
air".  DD is described as having a "dim look of satisfaction" before 
tapping the instrument with his wand again then the serpents 
vanished and he put the instrument back on it's table.

Does anyone have any theories on what this instrument is, who he is 
communicating with?  Is it a way of communicating with the Order? 
What does the comment "in essence divided?" posed as a question mean?

Again I am sorry if this question has been posted before but I need 
your help on this!!