When a guy is having a threesome with 2 chicks and he farts in one chick's mouth. That chick then proceeds to suck the fart in and blow it into chick #2's mouth. Chick #2 then inhales the fart and blows it back into the guy's asshole where the fart originated and they all continue fucking.

The safeguarding of Earth and other worlds from biological cross-contamination (i.e. billionaires with too much time on their hands).

Also known as “planetary protection.” Planetary protection / quarantine “reflects both the unknown nature of the space environment and the desire of the scientific community to preserve the pristine nature of celestial bodies until they can be studied in detail.”

There are two types of interplanetary contamination. Forward contamination is the transfer of viable organisms from Earth to another celestial body. Back contamination is the transfer of extraterrestrial organisms, if such exist, back to the Earth's biosphere.