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I think you misread me. My roommate was not 'jesting' when he threatened my cat. I meant that the LW's roommate seems like she's just joking around with the cats but that doesn't mean the LW doesn't have the right to request the behaviour to change.
If two people contract to live together in the knowledge that one person has pets they have to expect certain things like hair and litter boxes etc etc. The owner has to (or should in my opinion) clean up after them, feed and care for them so I think they have every right to suggest how they're handled. There is no common 'ownership', just common space shared by all. Hey, if the roomie pays for a vet bill or does clean up or feed them then she's got rights but otherwise no.