Here's how it works you are an alien parasite from outer space about the size of a slug as you crash land on Earth and your goal is to infect the people of Earth by taking control of their bodies whether by going into their mouths or their butt. When you infect them some of the humans may look normal while others have blank white eyes with slimy liquid drooling out of their mouths. Once the people are infected they now have the same goal as you to infect others but their method of infection is by kissing them to transfer their own parasite from their slimy liquid mouths into their mouths.

(You can start however you like)

Your small pod opened as you began to crawl around looking for someone to infect.