"Bad Luck": Sticking a Fork in Your Food

I'm not sure how my mom comes up with them(okay, I'm not sure how 98% of the things my mom says come from), but every so often she comes up with things that are "bad luck." One of them being that if you serve food to someone with a fork stuck straight up in the food, that's a terrible omen. Don't ask me why! And don't ask her why either... What my Korean mom says is, just IS!