I suppose they could have gotten a bug or two. This time of year with the windows finally opening, you never know what might crawl in. I found Fluffy playing with a dead bee yesterday morning. Don't know where it came from, but it hadn't died recently and I have seen them "chasing" some flying thing, I of course couldn't see it, but they can. Hopefully, it is nothing serious and will just run its course and be gone.