pftbest

The same law which makes gun recoil happen. If you fire a pistol in vacuum you would still get the same recoil or even stronger. The rocket engine fires a lot of gas molecules instead of bullets at much higher velocity than a bullet, which gives it the constant push/recoil

There are cases when electricians working on the street to restore power get shocked by some house generator feeding power back to the grid.

It can also be a hot water pipe, which gives out enough heat to protect the plant roots from freezing during winter.