Though my Chinchilla was just recently pregnant, she has always had a thing for laying on her side. The first time I ever saw it I thought it was the most hilarious thing EVER!
Just today though, she nursed her kits and then ran off and PLOPPED herself half on her side and half on her back...ha, it was so very random.
Her NEWEST thing though - her wooden hut is underneath of a ramp and she likes to stick her head out, look around, and then crawl on her back over the top and down the side of it!
SERIOUSLY! WHAT. IN. THE. WORLD!?!?
I call it her new trick because she seems awful proud of her flexibility!
My other Chinchilla Penny likes to come up to the front of the cage and do a weird little, jump-half-side-flip-THING??? and then she'll lay right on her side with her belly right up against the front of the cage door.
Their all nuts in my opinion
Here's a picture of Penny and Peekers when they were really young. Peekers is the White one and she was 6 months. Penny is the Standard and was 4 months. It was the first time I ever saw them cuddle.