Here's a question (maybe has been asked further back on the thread ... if so, please just ignore)
Suppose Noah had gone for a walk in the woods with his Grandma earlier in the week (surely this was not the only walk in the woods/maybe they visited Grandma often?) ... would the dogs be picking up old scents? I guess the obvious - they haven't found him yet - so even if the dogs are picking up scents, that doesn't really prove anything. Unless it was the one and only time he'd ever been in those woods ... however, if they said that positively NO scents have been picked up, well, that would be another thing.
(sorry if that's illogical)