Prelude

Anything can happen in the kitchen.
ANYTHING.  puke, sheeet, pee, garbage, food rolled on the floor and pick up to serve, sex, pubic hair, stepped on and serve, left overs from previous customer, and anything you can or can't imagine.   Many staffs "don't care/no time to care" about the job, the restaurant, or customers.  It's part of our society.

Just think of it as part of life, and it will help you build up good bacteria for future.
As long as they don't pour commercial chemical in the dish or serve nuclear fish, then we should survive.
PS.  Not all restaurants are like that, and for most restaurants, these doesn't happen regularly, but they do happen from time to time by accident, or on purpose, or just don't care.