People who have pets know how they are a part of your family.
I hadn't seen one of our cats in about 24 hours which was very strange, especially for this one. I went searching for her and came to find her curled up under my daughter's bedroom bed having passed away in the night I presume.
She was relatively young for a cat. I wasn't really prepared for her to be the one to pass as I have another cat I have had since college who is twice her age and very antisocial other than with me.