* Actually you do mishear people all the time. You figure out the meaning from the context. You may hear “bog” instead of “dog” but the sentence “the boy petted the bog” makes no sense—so you think dog. Moreover, even though you can hear sounds in the absence of airflow, puffs of air might make it easier to distinguish between two words such as “tall” and “doll” when there is a lot of ambient noise.

^† See http://sleightsofmind.com/media/McGurk. This is sometimes called the McGurk-MacDonald effect. It was first described in 1976 by Harry McGurk and John MacDonald in “Hearing Lips and Seeing Voices,” Nature 264: 746–48.