Bard Charm QuestionFollow

Solon's Song of the Sirens, according to what I read it is a charm song that lasts about 15 seconds. What I'd like to know though, that no bards I know seem to answer well, is is this a song that can be sung continuously, or is it a one-cast thing? Theoretically if it is a song you just leave running you can keep a mob charmed indefinitely, but it seems like the song would just stop when it tried to cast the next pulse and the mob is already charmed. Any bards out there that know the answer, please let me know.

On a side note, to all you forum vets, about six months ago I posted a thread asking about swarm kiting, and someone replied with a link to a flash animation that showed how swarm kiting is done. Anyone that can link to the thread or flash would be my new favorite person.