It's
This is not how you say "the flour belongs to the happy goat." No, it's not 'it's flour,' it is 'its flour.' Think of it this way: when you want to say "The flour belongs to that ten year old boy over there," you wouldn't say "The flour is his's," or "that's his's flour." No apostrophe, yo. For more help with your grammar, simply ask for it.