I dont know why i should think about it but i think when you are yawning your eyes dont reflect the anger! but if you are screaming either you are in panic or you are angry.. so, it must be easy to know for deaf people.

When you as a sharp-eared being hear both screaming and yawning your recognition will depend on the sound as well ,so the sight could be secondary in discriminating both. Deaf people's visual senses are very sharp and could distinguish easily between the facial muscles applied to yawn and those applied to scream. It is an unconscious analysis depending on kinesiology and facial expressions in recognizing those different patterns.

According to ScienceDaily (Mar. 2, 2009) www.sciencedaily.com/releases/2009/02/090227112311.htm Apart from looking at the person's gestures, lip reading is a critical means of communication for many deaf people, but it has a drawback: Certain consonants (for example, p and b) can be nearly impossible to distinguish by sight alone Tactile devices, which translate sound waves into vibrations that can be felt by the skin, can help overcome that obstacle by conveying nuances of speech that can't be gleaned from lip reading. Researchers in MIT's Sensory Communication Group are working on a new generation of such devices, which could be an important tool for deaf people who rely on lip reading and can't use or can't afford cochlear implants. The cost of the device and the surgery make cochlear implants prohibitive for many people, especially in developing countries.

"action speaks louder than words" the only thing is that the deaf must see the person doing either the screaming or the yawning. :)

i think that instinct will tell you. cowboy...