When my FI and I moved in together I brought the dog (Jack), he brought the cat (Turk).
Initially, the cat disliked the dog, so we always scolded Jack to be nice to Turk, and give him his space etc.
After about 6 months, and a lot of coaxing, they became friends.
At a recent vet's visit, my vet instructed us to put Turk on a diet (at nearly 20lbs). So in following the vet's orders, we did.
What did this cause? The cat decided he would eat his food, and the dog's food - and since put so much effort into teaching Jack to respect Turk, he won't protect his food, and thus continues to weigh 18.5 lbs.
They really aren't as stupid as we think.. lol.