Keller could even "hear" through touch. Sound produces vibrations. Keller could feel the vibrations and know there was a sound. The sound could be music or talking or walking. She could recognize the sound of a pencil falling or papers blowing off a desk.
With friends, Keller learned to read changes in their movement. She was so good at understanding her longtime teacher Anne Sullivan's movements that she would appear to be "hearing" the conversation, when she was actually interpreting Sullivan's physical reactions to the conversation.