In Us (2019), at the end of the movie we came to know that Adelaide was the clone for Red. Clones only shout throughout the film but Adelaide can talk like a human, how is that possible?
It's shown within the movie that when Adelaide is found by the parents after the incident in the fun house / hall of mirrors, Adelaide is mute. They visit a doctor. The doctor explains that after severe trauma, young children sometimes lose the ability to speak. That's actually just the doctor's diagnosis of what he thinks must have happened, when the truth is that Adelaide is a clone who has never been able to speak.
Adelaide is then given speech classes to learn how to speak "again". All of her clone-related personality traits (inability to speak, lack of normal social skills, possible unfamiliarity with the parents), are all attributed to her traumatic experience in the fun house.