Complex sentence: Rabbit eventually finds out that Pooh's bottom growing in fatness has actually caused it to become very comfortable and decides to use him as a chair, with his legs as arm rests and his obese-but-comfortable bottom as a cushion.
Split into simpler sentences: Rabbit eventually finds out that Pooh's bottom growing in fatness has caused it to become very comfy. Rabbit decides to use him as a chair, with his legs as arm rests and his obese-but-comfy bottom as a cushion.