Those lids have a couple of circular holes (for some purpose that remains unknown to me) and that little ******* found one of them. I usually remember to plug them, but not that time. I put machine screws through the holes and tightened with nuts on the other side.

Looking at the markings on that snake, it did remind me that it could have been a lot more serious.

ps. I felt dirty using the words "screw" and "nuts" in the original sense, is that normal?