Option 1.) it's the very start of the apocalypse and you're trying to save and protect friends and family

Option 2.) it's been awhile and you run into someone who's about to be devoured by zombies

Option 3.) you're a zombie but you're trying to communicate with the living that you don't want to eat brains and it's just a disease.

***Options 1 and 2 have zombies that eat brains and stuff unless you want them to have intelligence. Make sure your roleplay partner knows that.