Real dogs don't laugh. Here's a fun exercise... try to imagine what Snoopy's laughter sounds like. In the cartoons, it was always a weird kind of squeaky, babyish voice.
There was an animated version of the play You're A Good Man, Charlie Brown I saw some time ago, and it was notable for actually providing a voice to Snoopy's thoughts. This has always been the big things the comic strip has had over the cartoons; you don't hear what Snoopy is thinking, even as a disembodied voice. But that cartoon of the play did, and it was a really weird voice for him too. One could see how one could think of that as Snoopy's inner voice, but at the time it really didn't sound like it fit the character.
