Actor Richard Attenborough learned sign language to surprise a little girl
They say Richard Attenborough specifically learned sign language and didn't rehearse the scene with the girl in advance—so that her reaction on camera would remain authentic.
The little heroine, who can't hear, addresses Santa. And suddenly, he responds in her language.
In a second, something impossible to fake happens on her face:
confusion → recognition → shock → joy that makes your whole face tremble.
Not an "actor's smile," but the moment when the world speaks to you for the first time in a way that doesn't require you to guess.