To fold x To bend: Qual a diferença

I would rather use "flex the fingers/moving the fingers/move the fingers to side/curl the fingers/extend the fingers" etc... If comparing with a human being.
Since "bending" and "fingers" in the same sentence suggests some kind of (unwanted) contracture, disease or problem.

Folded arms and folded hands are usually found in writings about body language. Bending the knees is also common with the talking about posture and exercises.