When you see a claim that a common drug or vitamin "kills cancer cells in a petri dish," keep in mind:
[[A scientist stands on a chair next to a desk, pointing a gun at a petri dish. There is a microscope on the desk.]]
So does a handgun.

{{Title text: Now, if it selectively kills cancer cells in a petri dish, you can be sure it's at least a great breakthrough for everyone suffering from petri dish cancer.}}