I noticed earlier in the evening that Cosette was reaching up to the top of the used litter/compost container pulling at some old hay sticking out. This was not out of the ordinary. Sometimes she likes using the container as a place to stretch (similar to a cat).
Later in the evening, she managed to knock the lid off the container. But I was surprised to look over and see this:
I guess she just viewed it as a really really tall litterbox.
Meanwhile, Coco was unfazed.