Help Solve This Halloween Mystery

A dual-media-income couple I know came home yesterday to find blood splattered on their floor and walls. They own a dog and a cat, but both animals are fine, and the dog was penned up while they were gone. Another friend theorized that the cat is sneezing blood due to an upper respiratory infection, but the husband said some of the blood was fairly high up. Oddly, there was no blood on their furniture.