Unfortunately, there is not much to do, as you can't interact with anything in most cases. Still, you can communicate with other animals and crew, wander around the station, and go on a grand quest!
Animals spawn in various places as ghosts will take over the specific body of an animal. For the case of mice however, you'll usually spawn near a random vent, in Xenobiology, or in someone's office. If you can crawl through vents, they provide a useful means of escape from any pursuer.
Remember that you are in fact, an animal. But you can still play around with the crew and hopefully not be run over by mindless greytiders who appear very often!
You can be instantly killed by pretty much anything. The life of an animal is full of dangers!
Hiding somewhere or behind someone else is your best friend!
Return To The Dead
It's possible to return to ghost form if you happen to get bored or if you're killed. Don't expect your 'Repsawnability' to be back on once you ghost.