I had an oops moment this one time before I went off to school. Before I left every morning, I always turned off my TV with my remote and then gently tossed that remote onto my bed. But one day, I didn't see that cat lurking on the floor. I tossed the remote towards my bed, and she jumped right in front of it like a bodyguard protecting the president. It clocked her right in the head, making a funny CLUNK noise, and she ran straight outta there with a purpose. It was funny, but I felt terrible about it the whole day. Oops...  

The cats do plenty to injure themselves, I wouldn't worry about it!  Once when one of them was a kitten, it jumped up to the window and bounced it's head off the glass.

Then another time, the longhaired cat tried to jump thru a screen when it saw a squirrel outside, the screen frame got bent, I'm surprised she didn't break her neck!

Then there's the basement...they found a way to get into a space between the basement ceiling and the floorboards of the first floor.  Cats are strange, that's why they say "curiosity killed the cat" so I wouldn't worry about bonking them in the head by accident.

And don't even get me started on stepping on them in the dark. THEY are nocturnal, THEY can see us coming, and yet THEY do nothing but just sit there until their tail has a footprint on it. Then they act like its our fault.