Being insentient means having no ability to feel or understand. There's no need to apologize to an insentient chair leg when you accidentally kick it.
Insentient is the opposite of sentient, or "capable of feeling," which comes from the Latin sentire, "to feel." If something's insentient, it has no senses and can't feel physical or emotional pain or pleasure. People once commonly believed that animals fell into this category, but today most agree that animals are conscious, feeling beings rather than insentient objects. You probably think of trees as insentient, but some scientists suspect that even plants might have sensory abilities!