It sounds like something's changed for Charlie, and that could be new animals, people, or things.
The kittens are a good bet, as one of the things, but sometimes more than one thing happens at once.
For example, an injured deer. Imagine the sounds and scents from that to a dog.
Or, how about the deer that died in the neighbor's yard? Again, that's an overload of unusual scents, sounds, etc. Even the neighbors discussing it with one another, in what had to have been an unusual tone, is new.
Did they process it and keep the meat? Has Charlie ever been around when an animal has been processed?
And then, the possibility of another animal coming around that are not kittens.
So, mystery animal, people reacting to something, one or both deer, the cats and kittens, and goodness knows what else.
Did the dogs attack the other deer within' his hearing, do you think? I know that Krypto hears things across the canyon from us.
I think that those factors, plus the fact that the weather is no longer hot, etc. might make him more interested in the things going on around you now.
He is from working dog stock, so maybe he's just tapping into his inner hunting dog?
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