Curled pods: Any thoughts on why?

[mega]

I seem to have quite a few plants with very curled pods, like the ones below; any thoughts on what might be causing this?

 

[nitwit]

maybe some irritant or bacteria on the flowers and outsides
of them do the pods surfaces on the inside and outside
parts of the curls feel different?

is the color the same on the curled and not curled ones?

maybe cut open a curled and not curled and look for any bugs?

 

[millworkman]

I have noticed a few pods that do that, and after cutting them open noticed that the seeds on the side that curls in were not formed, they were just little black dots. So, maybe, this happens when seeds dont form so the pod doesnt need to grow on that side.