Enemies by nature?
Don't believe the hype. While popular culture would have us believe that cats and dogs are sworn enemies, there are actually plenty that cohabit just fine. Some opt for the diplomatic route, and just ignore each other, while others are truly good friends (like, sharing food level of good friends).
However, dogs and cats are very different. They communicate differently and have very different behaviors, so if you are planning to introduce a dog or cat to your home, you may need to give them a helping hand in the beginning.
Here are some tips to help Mittens and Rex get along together: after all, the happier they are, the happier you are.