First, let's establish the fact that <PERSON> doesn't ever talk. In the book My Life with Charlie Brown (Schulz Family Intellectual Property Trust, 2010), there's a chapter whose very title is, "What Do You Do with a Dog That Doesn't Talk?" In it, <PERSON> says,
<PERSON> doesn't even talk. In the strip he communicates by means of thought balloons.
If you study the strip carefully, you'll find that there seem to be exceptions to the "thought balloon" rule—e.g., on 13 Jan 1963 and 22 Feb 1955—but these seem to be inadvertent errors. There are also ambiguous cases where Snoopy is singing (16 Dec 1962, 6 Jul 1971) or barking (23 Dec 1989) but I think these are just meant to indicate that <PERSON> is making some audible sound, not actually speaking words. The one unambiguous case of Snoopy speaking (4 Apr 1952) is in a dream. So I think we can safely assume that <PERSON> never talks.
Okay, but can <PERSON> communicate telepathically? In earlier years, <PERSON> felt pretty strongly that the answer should be no. There are some illuminating remarks in Peanuts Jubilee: My Life and Art with Charlie Brown and Others (Penguin Books, 1975). On page 97, writing about his failed experiment with <PERSON>'s cat Faron, <PERSON> writes:
The cat and the dog could not talk to each other because <PERSON> never talks, he only thinks. 899
So I would have had to show the cat and dog thinking to each other, which was totally unreasonable.
Indeed, <PERSON> is totally silent, without even any thought balloons (though in the 24 May 1961 strip, <PERSON> wonders, "What do you say to cats?"). But a few pages later, <PERSON> explains how, when <PERSON> started to become a major character, he made a concession to allow telepathy in one direction (although he insisted on audible communication in the other direction):
A problem similar to that of the cat has now come about, and I have had to back off slightly. I would much prefer that <PERSON> not communicate with <PERSON>, but there are some ideas that are too important to abandon, so I have him speaking to <PERSON> through "thought" balloons. I've held fast with <PERSON>'s means of communication, though it has been tempting at times to have him talk.
<PERSON> doesn't use the word "telepathy" here, but there's no question that <PERSON> (and the other birds in the strip) can read <PERSON>'s thoughts directly. For an extreme example, on 11 Aug 1979, <PERSON> thinks, 'In the 1926 version of "Beau Geste," <PERSON> played <PERSON>…who played <PERSON> and who played <PERSON>?' <PERSON> answers, '<PERSON> and <PERSON>!'
However, despite allowing <PERSON> to read <PERSON>'s mind, for a long time, <PERSON> resisted having <PERSON> telepathically communicate with his siblings. For example, when <PERSON>'s brother <PERSON> was first introduced into the strip in 1975, <PERSON> was totally silent. Even as late as 18 Aug 1979, in a gag which demanded verbal communication between <PERSON> and <PERSON>, <PERSON> avoided having <PERSON> explicitly "think to <PERSON>." Eventually, though, when <PERSON> wanted <PERSON>'s siblings to play a larger role in the strip, he gave up all pretense and had them explicitly communicating telepathically. For example, on 8 May 1981, <PERSON> thinks, "Hey, what happened to all the doughnuts?" and his sister <PERSON> thinks, "You ate them!" Similarly, on 30 Sep 1982, when <PERSON> reunites with his brother <PERSON>, <PERSON> thinks, "How've you been?" and <PERSON> thinks, "Fine..how have you been?"
What about <PERSON> communicating with the kids? Well, <PERSON> is usually careful to ensure that the kids aren't literally reading <PERSON>'s mind. For example, in the two strips you cite, if you read them very carefully, you'll see that at no point do the kids have to "hear" exactly what <PERSON> is thinking; conceivably, they could be just making plausible inferences from careful observation of <PERSON>'s behavior. 417