I've learned to turn lights on because, as I said, my blackie Boo can't be seen at all. Even so, I still sometimes trip over him. Years ago I had a cat named Frisky who was always under foot and as I was closing the door, it stuck and wouldn't close. I kept trying to force it and guess why it wouldn't close? Because Frisky was there! She never made a sound, didn't cry out in pain or anything! And I didn't even see her! I felt awful, picked her up and hugged and kissed her and said "I'm sorry" over and over again but it didn't prevent her from doing the same thing later on. So don't beat yourself up; accidents happen. We would never hurt our furkids on purpose.