I'm sorry, this is our mistake. First of all, the posture should be lowered, to let the customer feel respected, and then for the sincere smile and language no one will throw face. Furthermore, you can offer to change the bowl of food, to ensure that the customer's continued trust. If someone is looking for trouble (may be small), change the dish to apologize on it, if not, do not private, the police it. However, for customers who actually have hair in their mouths, be humble. Also ensure that the next time the situation will not happen again. This situation, handled well, others will also feel good to see, if not dealt with, I am afraid that a lot of less repeat business.