Gerbil

Cody flopped onto his bed, not bothering to remove his backpack.

“Rough day?” asked Mister Fuzzbutt, pausing on his exercise wheel.

“We learned about pollution and climate change and stuff.”  Cody's voice was muffled by his Superman comforter.  “We're all going to die in a giant tidal wave after the planet turns into a desert.”

“Poppycock,” said Mister Fuzzbutt.  He groomed his ears.  “The temperature in here is lovely, and I keep everything very clean.”

“That's just your gerbil terrarium,” Cody said.  “I'm talking about the whole world.”

Mister Fuzzbutt gnawed on a toilet paper tube.  “I know my limits.”