Putting Down a Pet

[MrGiggity]

Just found out from the vet that my cat only has 2-4 weeks left before we should seriously consider putting her down. She is 15-16 years old and has bone cancer. The cancer is getting progressively worse and she is struggling to eat. This sucks. I like her more than 99.9% of humans. Does anybody have any experience with putting a cat down? When do you know it's the right time? Do they show any signs that indicate they are in great pain? I had to put my dog down 5 years ago but have yet to put a cat down. Just wondering if cats are any different. Thank you all.