Answer:
It goes up and down the stairs without moving.
What cleans as it gets dirty only to get clean the more you use it?
They can be long or short; they can be grown or bought; they can be painted or left bare; they can be round or square.
You can carry it everywhere you go, and it does not get heavy. What is it?
What is the center of gravity?
Those with eyes bigger than their stomach will definitely leave the restaurant with one of them. It is named after a house pet as well.