Answer:
I am an animal and a hair product
I spend the day at the window go to the table for meals and hide at night.
Soft hairy from door to door. I am the pet that always stays on the floor.
What gets sharper the more you use it?
I'm simple for a few people, but hard for them to hear. I live inside of secrets and bring people's worst fears. What am I?
No matter how little or how much you use me, you change me every month.