There's a stain on the ground, in front of his nose, faint and pale, a shadow of its former filth. He knows this particular stain very well; he's stared at it for many hours, as if a cat like him could feel sad. Helpless. The anger was immediate, of course, but when that left him guilt was the only thing to fill its hollow vacancy. Of all spots in this desecrated alley, Caligula would rather not be lying here, but his broken legs are slightly problematic, a small inconvenience. Many of his gang are dead, gutted as they slept, and he knows he will soon join them. As soon as the circle completes, pauses, begins again.
Tiberius appears in the mouth of the alley, perfectly hapless. He comes to halt on the stain before him, a memorial if there ever was one, and it's the signal. Caligula doesn't bother to tell him to get off. They'll be stains too, soon, and he doubts Drusilla would mind.
at least it was a blood stain and not any other kind of stain y'know