So far, we've only seen four inhabitants of Smileyland and have been given insight into the past of three of them, the other being the "guardian" of the place. What happened to everyone else?
The scene at the end of "Let's Play House" just seems like a naughty little joke, but the implications of the entire scene, from Mr. Cat rubbing his groin against Kaeloo's to the honking sound effect that played once the lights went out were rather unfortunate. In other words an attempt at rape had just been shown on-screen. Granted, the fact that she can transform into a hulking monster and beat the stuffing out of him lessens the impact, but it is more the idea that Mr. Cat might not be above raping his friend which is truly frightening.
Yoghurts are shown to be sentient in Smileyland. Quack-Quack eats them by the crate.
The Carnivore Confusion Mr. Cat must have as a result of constantly being around a duck, a squirrel and a frog.
Kaeloo's psychological profile in general. At times, to prevent herself from transforming into Bad Kaeloo out of rage, she forces herself into a wired-open grin. She also puts a lot of emphasis on being 'cute', 'sweet' and 'nice'. The fact that she was so overjoyed to die via being crushed by a meteorite in Let's Play the Quest for the Wholly Gruel indicates she may even be suicidal. Add to that her readiness to leave Smileyland in "Let's Play Courtroom Drama" when she decided her other personality was a serious threat to her friends and it quickly becomes clear that Bad Kaeloo is holding her hostage in her own body.
Kaeloo denies being a boy or a girl, but is clearly female. Then you remember that for some species of frog, gender isn't exactly a fixed attribute, and that hermaphrodites aren't a rare occurrence among amphibians.