Answer:
I can run but not walk. Wherever I go, thought follows close behind.
It's equally comfortable in an orchestra and a geometry textbook. What is it?
What is it that makes tears without sorrow and takes its journey to heaven?
Always old, sometimes new. Never sad, sometimes blue. Never empty, sometimes full. Never pushes, always pulls.
What goes in, but never through? I've got some and so do you. We might lend one, or even two, but only if our trust is true.
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.