I had a camera set up at a water-hole recently and returned to find it covered in mud. Not just a little muddy, but plastered with mud! The sensor and flash cover were caked with the stuff but, luckily, the lens appeared clear. I was pretty sure that a warthog (Phacochoerus africanus) had done the dirty deed since the camera was mounted at a height of about 40cm. Warthogs are great wallowers and love to rub off the mud on a convenient tree or stump.
However, when I saw these images I soon realized that one shouldn't presume anything too quickly!
It was a youngish black rhino (Diceros bicornis) and they're usually not very respectful of human property. I'm grateful that I still have a camera in good working order.