Our culture phrases damn near everything in metaphors of war. The war on drugs. The battle of the bands. Bob lost his battle with cancer. It's absolutely pervasive, to the point it's almost as invisible as the air.
WARNING: Dunkin Donuts can expose you to chemicals including Dihydrogen Monoxide, which is known to the State of California to cause cancer. For more information go to www.P65Warnings.ca.gov.
This is a joke about Einstein's form of the Equivalence Principle:
https://en.m.wikipedia.org/wiki/Equivalence_principle