Damn brigs back memories of when I was 10 and a friend of mine found a cat that drank antifreeze and was very sick. He asked me to help him carry the cat to the vet clinic which was about three blocks away. At the vet (first time I was ever at a vet) the doctor look the cat over and said it was not going to make it and would have to be put down. She also asked us whose cat it was and that there was going to be a charge ($200 zloty - Polish money) I said I would pay for it but would have to come back with the money in a few days.
She then injected the cat with something. The cats breathing slowly slowed down until about a minute later when it made this huge gasp for air and everything stopped. I've never seen anything like that before its was quite terrifying/upsetting and I was use to killing chickens (cut their heads off) on my grandparents farm when my grandma needed one for chicken soup.
After seeing the cat take is huge last breath my view on killing animals was never the same.