In pirates of the caribbean 3?

at the start of the movie, why does lord beckett say "finally" when the people about to be hanged start to sing?

He wanted the prisoners to call together the Brethren Court, which could only be done by singing that pirate song.

Edit:
I can see where the poster below is coming from, but remember that Beckett wants to completely rid the world of piracy, that's why he was executing so many people at the beginning of the movie. He wanted the Brethren Court called together, which would convene all the pirate lords, and he didn't know of any other way to do it aside from having the prisoners sing the song. Once they started singing he said "finally" because he knew the pirate lords would come together at Shipwreck Cove, and then he'd be able to take them down as a whole.

Beckett hates pirates with a vengeance. He's probably saying "finally" because he's glad to see some pirates and/or people accused of assisting pirates get what he sees as a well-deserved date with a noose.

EDIT - Chrissy is correct that the song was needed to convene the Brethren Court, but I don't think that was the reason Beckett said "finally."

EDIT again - After further consideration, I think Chrissy's answer is spot-on. If the question goes to voting, she's got my vote for Best.

Possibly its because it signifies that they have given up on their human lives. Seeing as the song says "We shall never die" or somthing like that..Maybe they will go the gallows without a fight now. Thats my best guess!

he knows the pirates will take action when the song is sung and the little boy drops the coin when he is hung which leads in to barbosa and elizabeth at singapore and barbosa hold the coin up to the guys ear saying the song has been sung.