One of my cats had to be put to sleep 3 months ago with renal failure. Just after she had been diagnosed my other cat (same age -15, & sister of) started eating less & has almost totally gone off wet food & mostly eats dry . She has lost about a third of her weight- she was quite tubby, so not too bad from that point of view. However she has now taken to sitting in the middle of the room now & again & making quite strange crying sounds. Do cats feel the loss of another cat & could this behaviour be part of that or something more serious.? I have had her 10 years & the only vet visits have been for annual boosters so I think she is still in good health.