The reference is the nightingale in "Try and Catch Me." I think Abigail was just testing to see if Veronica could hear the tape recorder through the safe, to make sure that nobody would be able to hear Edmund's screams.
thank you, E! i never got the connection to the tape recorder before. okay, now it makes sense.
You can add this: "I guess your bird has flown, eh Columbo?" - Dirk in Dagger of the Mind, explaining that Columbo's theory is no good.