You'll want to head to Krasarang Wilds for this particular item, called Feverbite Egg Sac. It's exactly what it sounds like -- the egg sac of a spider named Feverbite. However, in order to get the egg sac, you've got a little work cut out for you. Feverbite spawns in the Krasrang Wilds at coordinates 18,45. She won't be there when you arrive, unless someone else was working at making her appear. But you will find a cobweb-coated copse of trees with dozens and dozens of creepy little Feverbite Hatchlings running around.
So how do you force mama to make an appearance? By killing her precious little babies, of course. The hatchlings have very little health, so just run around the trees and spam AoE attacks to mow them down. You'll have to kill a lot of these things to make Feverbite spawn, so just concentrate on clearing out the area. Eventually, Feverbite will make an appearance atop a small hill in the center of the clearing, at which point you can either fight her, or get thoroughly creeped out and run away. Up to you!
Feverbite is a level 87 elite mob. She's incredibly easy to solo, but she does have one trick -- she'll summon a gigantic swarm of her hatchlings while you're fighting. These are the same hatchlings you were just killing in one hit, so you can simply AoE them down and concentrate on murdering their mother. Once killed, Feverbite will drop her egg sac, suitable for terrifying any unsavory individuals you encounter.
Note that this item is not a trinket, so you don't need to equip it to use it. However, much like the other fun items scattered around Pandaria, it only has three charges. If you run out, you can always duck back into the forests and murder some spiders to fetch another one. While the Feverbite Egg Sac isn't a cosmetic item like others you can find around Pandaria, it's still certain to be a conversation piece. Even if that conversation is limited to "Aaaaugh get it off me!"
... well at least they're saying something, right?
Mists of Pandaria is here! The level cap has been raised to 90, many players have returned to Azeroth, and pet battles are taking the world by storm. Keep an eye out for all of the latest news, and check out our comprehensive guide to Mists of Pandaria for everything you'll ever need to know