When you lose a family member, furry or otherwise, you always expect that there are going to be big things you miss. A cuddle buddy on cold nights, that way they used to fuss over you when you were sick or upset. In fact one of the first things I realized when Simba passed was that she always made a fuss over me when I was upset about something... and now the reason I was upset was because she's not around to fuss over me anymore.
But it's the little things that really get you. Those little habits you never really noticed that catch you by surprise and bring the tears back all over again. It's going to say hello to her when I first get home. Automatically glancing at the bed when she's not in the living room. Walking by her favorite chair and looking over to watch her sleep, and finding it empty. The sleepy look she used to give me when I opened the blinds in the morning... the grumpy one she gave me when I closed them at night. Things you never realized you had come to expect until they're gone.
Just today I opened the treat drawer, looked at Anubis, and said "I need to go get more treats for you guys." Never mind that just before that, I was wondering what to do with the Greenies now since he won't eat those (Simba loved them). Old habits die hard... and here I sit crying again because of it.
Only when they're gone do we come to realize that the little things are what makes someone who they are. And then those are the things that tear at your heartstrings most.