I've found one of the above holes in my window screen in the last few months. The obvious correlation was that they only appeared in the screens of the windows that I keep open in the summer months for the cats to sit in. However, my cats (for reasons unrelated to me) do not have front claws, so it wasn't like they were clawing to get out. I had no idea where they came from, so I just closed that window and opened a different one (in case it was the cats trying to get out). A few nights ago, I heard an angry yowling and came out of my room just in time to figure out what was going on -- a neighborhood bully cat was trying to jump in the window to (I assume) attack my cats. He obviously does have claws and he's ripping the screen as he hangs on before dropping off again (that's where the second photo is from). Son of a bitch. It's things like these that make me glad my boys don't go wandering around the neighborhood by themselves!