The University of Illinois Extension service says you should harvest beans when the pods are firm and have reached their full length.

VOA: special.2009.03.24

There's loads of different kind of pods all around London

伦敦到处都有很多不同的租车点，

伦敦的蓝色自行车 - SpeakingMax英语口语达人

Green bush beans used to be called string beans because of fibers along the pods containing the seeds.

VOA: special.2009.03.24

Bean plants produce more beans if pods are continually removed before the seeds are mature.

VOA: special.2009.03.24

The seeds float in the air when the pods break open.

VOA: special.2010.04.06