Cats, Schmats.
I wonder if you can cook 'em?
I've had a few since I was a small child and I have to say I wouldn't have one again if it was my choice. Yes, they can be lovely company and fun and cute so might be worthwhile if I was stuck in the house as a lonely OAP. But they're usually more trouble than they're worth and costly.
My last two were inherited from sister-in-law who split from boyfriend, went travelling and then moved into a flat which wasn't 'appropriate' for cats due to it being on an main road and we (wife and I) reluctantly agreed to have them. Within 6 months she had another cat and refused to take the other 2 back (I suspect they reminder her of her former boyfriend who was God on earth - but still slept with a workmate - not sure how you do that; she loved him, in-laws loved him even though he had gone on a Shagfest, but that's another story). Divine retribution arrived when aforesaid third cat got run over. Yes, I felt sorry for the cat, but I can't say I didn't smirk at the news.
Moral of the story - is there one? Don't trust your wife's sister (or her boyfriend).