I wonder what this magic is....

[M.Clifford]

No: HPFGUIDX 102805

In OotP on page 10 of my edition printed in Australia, I found 
this...

" 'Get - off - me!' Harry gasped. For a few seconds they struggled, 
Harry pulling at his uncles sausage-like fingers with his left hand, 
his right maintaining a firm grip on his raised wand; then, as the 
pain in the top of Harrys head gave a particularly nasty throb, 
Uncle Vernon yelped and released Harry as though he had recieved and 
electric shock. Some invisible force seemed to have surged through 
his nephew making him impossible to hold. " 

Further on a paragraph suggests that Uncle Vernon had Harry in some 
type of stranglehold which in turn suggests that Harry may have 
internally percived a threat upon his life here.

What I would like to discuss is which magic is this that created the 
invisible force surging through Harry. 
Unlike the incedent with Aunt Marge no further mention of this event 
was made by anyone in the Ministry or otherwise authorative. Almost 
as though nobody knew it had happened..... but for us readers. 

Is this possibly the power that the Dark Lord knows not? Is it the 
protection of Lily extending beyond Voldemort?

Suggestions..... comments........ rebuttals......???

Valky