I caused the death of my 17 year old Chipin, Dobie, by using a rug shampooer that had for some reason gotten much louder and shrill (even though not full). Normally, I would put him and my poodle out in the carport while I shampooed, but this time, darkness had set in and it was just for a few swipes back and forth to clean up a spill, so I thought it would be ok.
Dobie jumped around the shampooer looking alarmed, but I thought my sing song voice of, "It's ok, mommy is almost done" would assure him it was ok.
Well I had pushed it probably 5 swipes back and forth, turned it off, heard a small yelp and looked for Dobie. There he was, dead in the hallway, my little boy dog. =(((( I sobbed and petted him for I don't even know how long, praying for him to "wake up". I didn't exactly see him die, but it was still traumatic and still affects me daily, although it's been over 2 years now.
I have not seen other animals die, but only have found them after death. It's very sad, either way.