"Laut" can mean "sound" and "Gebarden"/"Gebärden" are movements. I instantly have to think of hands when I read this because deaf people use "Gebärdensprache" - speak with hands.

It is a teaching concept for kids in elementry school. They are learning the spelling of words by doing certain gestures according to a letter. Each letter of the alphabet has a gesture and they gesture the spelling of a word.