Cubile Animus, (Latin for "Nest of souls"), is an ancient and power artifact (a small box of sorts) buried in the mysterious city of Whitechapel. It has the power to trap and contain souls.
Jesse, also known as Horace Reverand Black, wanted to find the box so he could use it to revive the Black Army, his evil 219 followers that were burned alive at a stake. He planned to do this by taking the souls from the 219 Duskers at the advance screening of Dusk III: Unbitten and transfer them into the box to recreate the Vampire Army. Ethan, Benny, and Sarah stopped him by opening the box with the souls inside and letting the vengeful souls fly straight through Jesse's heart, killing him.
Jesse was later revived and resurrected from the dead when Ethan, Benny and Rory dug up the box to trap a demon spirit that had taken possession of Sarah's body and dropped it to the ground while digging. After being reborn, Jesse vowed revenge on Ethan and Benny and to make Sarah a true blood sucker, vampire. Follow Up: My Babysitter's a Vampire: The Complete 1st Season