behind one's hands

[ovvpapatya]

The silvery girl was drawing backwards away from
them, her hands over her mouth, and her eyes huge in
that pale face surrounded by strange, dark, wet-looking
hair. She was muttering something behind her hands,
and Rose had to lean forward to catch what she was
saying.

Does "behind her hands" mean here that she tied her hands at the back?

 

[Barb_D]

No, her hands were in front of her mouth, so her mouth was behind her hands. She was saying something, but her hands made if hard to hear what those words were.