First, vision in humans is genetically engineered to pay attention to the face, and to pay attention to movement. Babies watch their mothers faces, and humans as a species spent a remarkably large fraction of their mental capacities watching and interpreting each others' faces. Perceptual systems also are especially sensitive to movement, and humans are not much different from other hunting animals, for which visible movement is instantly the total focus of concentration. The speaking mouth, of course. It follows that humans are genetically engineered to pay special attention to lip synching.
Lip reading is little short of miraculous.
To infer sound from vision is an amazing feat. Yet many deaf and some hearing people can do it pretty well. This could only be true if humans were highly sensitive to lip movements. Second, sound is the main source of communicated thought and feeling. Human thought is expressed and communicated from person to person by a genetically engineered system that uses the medium of sound, namely language itself.