Nabsack
A tiny beaver that lives on your hip is called a nab. The bag it lives in is called the nabsack. You can only see it with a special x-ray that makes you feel like you're going to puke.
'I saw a nab on my hip. It looked at me like it was going to eat me.'
'My x-ray showed me a nab inside my nabsack. I now have a beaver living in my pants.'
'Your nabsack is so smelly, I think it's got a second job as a garbage truck.'