Gravity responds to all kinds of energy, whatever form that energy may take. ... These so-called disconnected graphs, or vacuum bubbles, are the Feynman diagram analogue of zero-point motion.

I see the notorious CVCC Vacuum Hose Routing Diagrams beneath the hoods of mid-80s Hondas all the time when I visit wrecking yards, and now I've managed to score a genuine NOS underhood decal.