You don't need your hands....do you?

Did you ever have a teacher (or several) who would tell kids who waved their hands around too much while they were talking that they should sit on their hands and try to make their point with words alone? And these kids would have such a difficult time...sometime one of their hands would sneak back up for a gesture without their even noticing.

The other day I saw two young women engaged in an animated conversation on the subway. By observing them I could tell that neither was seriously hearing-impaired (no hearing aids, perfectly normal speech, not always watching each other's lips, responsive when they were getting off and the one continued speaking behind the other, etc.) and yet one of them was signing everything she said. Not gesturing, signing. I wonder whether she has a family member or close friend who is deaf, and, having learned to sign whenever she speaks to them, finds it hard to break the habit when speaking to someone else? And I wonder how long she's been doing it. And I wonder, if she was doing it when she was a kid, whether she ever had a teacher like that...