Almost Twins

These are things Fred and Celia have in common-

They both complain that they are hungry all of the time.
They both like to have their tummies rubbed.
They both like having a bath.
They both have sharp nails.
They both fuss when I try to deal with said nails.
They both like to ride in the car.
They both have wonderfully comfortable beds of their own.
They both sleep in our bed instead.