Answer:
I open wide and tight I shut, Sharp am I and paper-cut fingers too, so do take care, I'm good and bad, so best beware.
What do you fill with empty hands?
What goes in the water black and comes out red?
What has three feet but no arms or legs?
I am the red tongue of the earth, that buries cities.
If you can spot one of these eastern warriors, it means they're not doing their job right.