Other How can I tell?

You can do a simple test when Rodolfo's back is turned. Call him by name or clap your hands behind him and see if he turns to look at you. If he doesn't respond after repeated attempts, I would take him to a vet to have a hearing test done. The hearing tests I'm aware of are the BAER or BAEP tests and they can be useful in determining deafness.

I had a Panda ferret. We never had her tested but I think she was deaf. She didn't respond to any sounds. I think they sleep heavy but the house next door could had blown up and she wouldn't have woken up.

Ok they are both going to the vet for distempers this friday so I will have Otis tested. Thank you!