Watch a honey bee's venom sac continue to pump venom after detaching from the bee.
In this video, the sac pulsates while it's lodged into someone's finger for a few seconds as if it has a mind of its own. A sting in the finger like this one looks pretty unpleasant. I'd have wanted it out immediately.
From Youtube: "When a bee stings, the part of the bee's body containing the stinger and venom sac tears off and remains. The venom sac continues to pump venom."
See also: 15 million bees let loose on highway following truck accident