My little piece for Let Down! I've seen a lot of people just use feathered or bird wings, which confuses me a bit. The lyrics suggest a metaphor which is more related to insects. Crushed like a bug in the ground. Shell smashed, justices flowing. Wings twitch, legs are going. I believe the "chemical reaction" is more akin to a moth or butterfly metamorphosis. Growing wings from being in such a dark place (chrysalis/cocoon) for so long. So!
Regarding the actual piece l've chosen Luna moth wings, as they are a symbol of rebirth.