How can a trouser pocket be empty and still have something in it?

A trouser pocket can be considered empty if it doesn't contain any significant or recognizable item, such as money or a phone. However, it may still have small debris, lint, or crumbs that are not immediately noticeable. Additionally, it could hold an item that is not typically associated with being "something," like an old receipt or a loose thread, thus rendering it practically empty in terms of functional use.