They definitely grieve and poor Jaffa grieved for some time when his brother, Magpie, died. Even though they weren't all that close, I think Jaffa missed the companionship. Magpie died in the October and it wasnt until I was forced to take Jaffa up to my mum's at christmas that year (left it too late to book him into a cattery) that things got better. When we got home, the change seemed to have worked and he started to act more normally. I don't know how long it would have taken if he hadn't had that disruption to his routine. Jaffa became very clingy and wouldn't let me out of his sight. he wouldn't even sleep on the bed in the bedroom whilst I was next door - he had to be with me all the time.