Okay. To start off, I'm posting this here instead of exploits because i see it as a smart use of game mechanics and not an exploit.
But on topic...
This guide is about, Sorrowsong - Item - World of Warcraft. It will only proc off the target you are attacking it it is bellow 35%, however, you can get it to proc before and during a boss fight without the boss being 35% or below (or any mob).
If there is a critter around all that has to be done is kill the critter and you get the buff. So, if there are multiple critters in the boss room all you have to do is kill one every 20 seconds and the trinket is used to it's full potential.
Sorrowsong drops off http://www.wowhead.com/npc=44819 in Lost City of the Tol'vir.