I never saw anything that I thought could be mantis poo. I never saw anything of them actually use the 'facilities'. This may be due to the fact that mantids are much more mobile than web-based spiders, and so anything they did leave behind would have been scattered about and much harder to spot. I did have to pick up after them though because mantids are notoriously sloppy eaters. Since they eat their prey alive, the squirming around sometimes causes premature dismemberment. If the mantis drops a body part, or even the whole meal, it won't bother retrieving anyting. Plus, they will often eschew things like legs and wings for a nice meaty abdomen or head -- dropping the unwanted pieces form wherever they are eating. When catching stinging fliers (wasps/bees/etc) the mantids would catch the head in one claw and the abdomen in the other, right next to the stinger so they couldn't get stung. I'm sure this was no accident. From there, they would frequently chew their way through the midsection and proceed to eat from the inside out, dropping the empty husk to the floor. Spiders too -- except they would usually make efforts to avoid the head, and would usually try to immobilize at least the rear legs.

I just kept a dustbuster handy -- and didn't use it for anyting but cleaning up after the mantids.

As far as the cat goes, she was constantly aware of the mantis I had at the time, greatly intrigued by it, and extremely wary of it. That one was more then six inches in length, probably the biggest, fiercest one I have ever kept. So I know she could see it even when it was still. (Even when they're 'still', mantids aren't still. Like many camouflaged tree-dwelling predators they tend to wiggle back and forth to simulate movement by the wind. Especially evident when on the hunt.) I never saw such a thing, but I do think that the mantis struck the cat. It sure doesn't feel very good, and I imagine it hurts more on a smaller organism.