How does DD know what Petunia/Vernon said?

[Tonks]

No: HPFGUIDX 156726

BettieTheBookWorm:

> Could it be that there is a photo on the wall somewhere of a wizard 
who alerts DD when Harry is in trouble?  Perhaps Petunia has been 
forced to alter her beautiful decor in some way to allow a wizard in to 
watch over Harry.
> 

Tonks:
I agree with whoever said that DD just understands human nature and 
expected that Vernon and Petunia would have those feelings of wanting 
to get rid of Harry after Dudley was attached.

But while we are on the subject. Remember once DD said he didn't care 
what they did as long as they didn't take him off the chocolate frog 
cards.  I think that is how he knows what is going on in many places 
around the school or where students are who have a collection of cards. 
Course that are many portrats around as well. But I suspect the frog 
cards are important too.

Tonks_op