Working on the assumption that keys do double duty as  a phallus, then what’s the importance of a glass key?  A key’s function is to unlock something meant to be private, secret and reserved.  However, if a key is made of glass it could break into jagged shards and ruin the very thing it’s supposed to protect.  Interesting binary.  In “The Glass Key,” the binary is reversed in that Veronica Lake holds the key.   In fact she seems to want to unlock it herself and reveal the mystery.  Yes, she’s a take charge kind of girl who “Can handle ’em both.”