Lip reading is cognitively tiring, even if you don’t realise it is. Context and clarity help a lot, but even in a completely silent situation, it would be difficult to lipread every word accurately. If you add extra noise that the brain is still registering or trying to filter out, it makes it even harder. Add to that, not everyone shapes the same word in the same way depending on accent; reading lips on people with facial hair can add challenges; lots of words sound similar and the brain uses other clues to understand the meaning based on context and tonal shift. I say to my friends that trying to lipread in a noisy environment would be like them trying to concentrate on speech while someone was constantly poking them. 
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