We really wish we knew what happened in the front downstairs hall (the passage to left of the bathroom door in the background to the photo) this afternoon.
When I came downstairs to feed the boys I found fresh dried blood splatters between the counter and the bathroom door. +Katherine Derbyshire said that it looked like a feline slasher movie.
Most of the blood was on the floor in front of the door, but we found individual droplets everywhere from 3+ feet up on the bathroom door to on the counter (where the boys are sitting on in the photograph), and into the living room (to their right). There was no real trail, just droplets here and there.
It was bright enough to be arterial blood.
We were out most of the day, but Katherine thinks there was no blood when we distributed kitty treats when we got home.
We didn't hear any battles royal between cats.
There are no marks on any of the cats. We checked each at least twice.
There no signs of invading rodents.
Short of putting the blood through a DNA analysis to determine the owner, we have no clue.
Update: Actually a little bit of a clue. Given the lack of interest in the blood by the resident felines, we're guessing it belonged to one of them, not a rodent.