I loved this story when I saw it. It reminded me of this white cat that used to live near us years ago. We would buy catnip toys (one particular one) for our cats, and this cat would come into our place and take them. We were forever replacing them. By chance we finally met the owner and found out that white cat (we called him Thiefy) had a huge stash of these toys and that the lady never knew where he got them from.
IM so sorry for your loss … it almost sounds like feline leukemia or feline aids... we had 2 litter mates die from it... And the symtoms you describe sound all to familar ... You might contact your vet and ask questions... If you have other cats, this is a highly contagious desease.
