Maybe they weren't speaking English. Maybe they were all speaking in their normal animal-language and the movie just translated it for the audience!
For all we know, Mowgli could have been sent to an insane asylum for growling at everyone like a bear-panther-snake-monkey-tiger when he went to go live with the humans.
That girl at the end of the movie: "Oh, hello there!"
translated for the audience
the jungle book took place in india...
In the book he actually spoke their language.