So I'm a total pet-drug-pusher. I had a cat who seriously jonesed for breve (half-and-half) so I gave her a milliliter a day. My dog today needs peanut-butter like it's the ambrosia of the gods. It's a small treat every once in a while.
Out of respect for your friends of fur, allowing them a small dose might enhance their enjoyment of life a bit, especially since we are social beings who enjoy sharing a meal with each other. And unlike half-and-half, cats can actually digest tuna.
My cats are dum though. I'll crack open a can of tomatoes and they freak out thinking it's dinner time. I let them sniff it, but then they look confused.
Same when I'm getting some Tums. They think it sounds like greenies.
Oh, man. The amount of times I'd exasperatedly repeat to my cat "it's beans!" or someone similar and let them smell the can I'm opening. I know you know this doesn't smell like tuna, you fuzzy idiot...
I trained my cat to eat plain chicken by tearing off little pieces and any time he didn't go for it I'd make sure he watched me eat a little. Do that, offer him the other half of the piece I ate, repeat a few times. Now he knows whenever there is a new food if I'm trying to give it to him and I take little bites that he should try it too. It's a lot of fun
"Jones" is an American slang word meaning to be addicted to something, so "jonesing" for something means to crave something very strongly, and generally very vocally.
"Breve" is a coffee drink that is commonly made with half-and-half, which is a product that is equal parts cream and milk. I assume that people have taken to using the term to refer to half-and-half itself, but I've not personally heard that.
So the sentence is saying that their cat was addicted to half-and-half and would act like a junkie doing anything to get their next fix.